Thin film piezoelectric resonator, thin film piezoelectric device, and manufacturing method thereof

ABSTRACT

A thin film piezoelectric device includes a substrate ( 12 ) having via holes ( 22 ) and a piezoelectric laminated structure ( 14 ) consisting of a lower electrode ( 15 ), a piezoelectric film ( 16 ), and an upper electrode ( 17 ) formed on the substrate ( 12 ) via an insulation layer ( 13 ). A plurality of thin film piezoelectric resonators ( 210, 220 ) are formed for the via holes ( 22 ). The piezoelectric laminated structure ( 14 ) includes diaphragms ( 23 ) located to face the via holes ( 22 ) and a support area other than those. The thin film piezoelectric resonators ( 210, 220 ) are electrically connected by the lower electrode ( 15 ). When the straight line in the substrate plane passing through the centers ( 1, 2 ) of the diaphragms ( 23 ) of the thin film piezoelectric resonators ( 210, 220 ) has the length D 1  of the segment passing through the support area and the distance between the centers of the diaphragms of the thin film piezoelectric resonators ( 210, 220 ) is D 0, the ratio D 1 /D 0  is 0.1 to 0.5. The via hole ( 22 ) is fabricated by the deep graving type reactive ion etching method.

This application is a 371 of PCT/JP2003/007857 filed on Jun. 20, 2003,published on Dec. 31, 2003 under publication number WO 2004/001964 A1which claims priority benefits from Japanese Patent Application Number2002-179910 filed Jun. 20, 2002.

TECHNICAL FIELD

The present invention relates to a thin film piezoelectric deviceprepared by combining a plurality of thin film piezoelectric resonatorsutilizing piezoelectric thin films and, in more detail, relates to athin film piezoelectric resonator for use in a filter for acommunication apparatus, a thin film piezoelectric device, and a methodof manufacturing the device.

Moreover, the present invention relates to a thin film piezoelectricresonator utilizing a piezoelectric thin film for use in broad fieldssuch as a thin film filter for use in a mobile communication apparatusor the like, a duplexer or transmission/reception switching unit, a thinfilm voltage control oscillator (VCO), various types of sensors and thelike, a device using the resonator, and a method of manufacturing thedevice.

BACKGROUND ART

A device utilizing a piezoelectric phenomenon has been used in a broadfield. While miniaturization and power saving of a portable apparatusadvance, use of a surface acoustic wave (SAW) device as a filter for RFand IF filter has been increased. An SAW filter has met user's strictlyrequired specifications by improvement of design and productiontechnique, but improvement of characteristics has been nearly limitedwith increase of a utilized frequency, and a great technical innovationhas been required both in miniaturization of electrode formation andsecurement of stable output.

On the other hand, in a thin film bulk acoustic resonator (hereinafterreferred to as FBAR) and stacked thin film bulk acoustic resonators andfilters (hereinafter referred to as SBAR) utilizing thickness vibrationof a piezoelectric thin film, a thin film mainly constituted of apiezoelectric material, and electrodes for driving it are formed on athin support film disposed on a substrate, and basic resonance in agigahertz band is possible. When the filter is constituted of FBAR orSBAR, it is possible to achieve remarkable miniaturization, lowloss/broad band operation and integration with a semiconductorintegrated circuit, which are expected to be applicable to a futureextremely miniature portable apparatus.

A thin film piezoelectric resonator or vibrator such as FBAR, SBARapplied to the resonator, filter or the like utilizing the elastic waveis manufactured as follows.

A substrate film or base film made of a dielectric thin film, anelectric conductor thin film, or a laminate thereof is formed on asubstrate of a semiconductor single crystal such as silicon, polycrystaldiamond formed on a silicon wafer, insulator such as glass, or aconstantly elastic metal such as elinvar by various thin film formingmethods. A piezoelectric thin film is formed on this substrate film, andan upper structure is further formed if necessary. After forming eachlayer, or forming all layers, each film is subjected to a physical orchemical treatment to thereby perform patterning and etching. Asuspended structure in which a portion positioned under a vibrationportion is removed from the substrate is prepared by anisotropic etchingbased on a wet process, thereafter the obtained structure is separatedby the unit of one device if necessary, and accordingly a thin filmpiezoelectric device is obtained.

For example, a thin film piezoelectric resonator described inJP(A)-58-153412 or JP(A)-60-142607 is manufactured, when a substratefilm, a lower electrode, a piezoelectric thin film, and an upperelectrode are formed on the upper surface of a substrate, thereafter avia hole is formed by removing a portion of the substrate under aportion constituting the vibration portion from the lower surface of thesubstrate. When the substrate is made of silicon, a via hole is formedby etching and removing a part of the silicon substrate from the backsurface using a heated KOH aqueous solution. Accordingly, a resonatorcan be prepared having a configuration in which an edge portion of astructure consisted of a layer of a piezoelectric material sandwichedbetween metal electrodes is supported by a portion around the via holeon the front surface (upper surface) of the silicon substrate.

However, when wet etching is performed using alkali such as KOH, sideplanes of the via hole are inclined 54.7 degrees with respect to a (100)silicon substrate surface because the etching proceeds in parallel with(111) face, and a distance between centers of adjacent resonators has tobe remarkably enlarged. For example, when a resonator having a vibrationportion with a plane dimension of about 150 μm×150 μm is constituted ona silicon wafer with thickness of 300 μm, the resonator requires aback-surface etching hole of about 575 μm×575 μm and the distancebetween the centers of the adjacent resonators is 575 μm or more. Thisinhibits high density integration of an FBAR resonator. Moreover, whenmetal electrodes disposed in such a manner as to sandwich apiezoelectric thin film are extended to connect adjacent resonators,electric resistance increases because of longer distance of the metalelectrodes. Therefore, there is a problem that insertion loss of thethin film piezoelectric device prepared by combining a plurality of FBARresonators becomes remarkably large. An acquired amount of finalproducts, that is, the number of thin film piezoelectric resonatorsformed per unit area on a wafer is limited, and a region of about 1/15of a wafer area is only utilized for the resonator to produce devices.

A second method of the conventional technique to manufacture thin filmpiezoelectric resonators such as FBAR, SBAR applied to the thin filmpiezoelectric device is making of an air bridge type FBAR device asdescribed, for example, in JP(A)-2-13109. Usually, a sacrificial layeris disposed at first, and next a piezoelectric resonator is produced onthis sacrificial layer. The sacrificial layer is removed in or near theend of the process, and the vibration portion is formed. Since allprocesses are performed on the wafer front surface, this method does notrequire alignment of patterns on the opposite surfaces of the wafer or alarge area opening in the back surface of the wafer. InJP(A)-2000-69594, a constitution and a manufacturing method of an airbridge type FBAR/SBAR device using phosphor silicate glass (PSG) as thesacrificial layer are described.

However, in this method, a long complicated step is required. That is,after a series of steps of formation of a hollow in the front surface ofthe wafer by etching, deposition of the sacrificial layer on the frontsurface of the wafer by a thermal enhanced chemical vapor deposition(CVD) method, planarization and smoothening of the wafer surface by CMPpolishing, and deposition of the lower electrode, the piezoelectric thinfilm, and the upper electrode and formation of the pattern on thesacrificial layer, a via (hole) extending to the hollow is made, anupper structure deposited on the front surface of the wafer is protectedby a resist or the like, and an liquid etching reagent is penetratedthrough the via hole to thereby remove a sacrificial material from thehollow. Moreover, the number of masks for use in forming the patternlargely increases. As the manufacturing step is long and complicated,the cost of the device is increased, yield of a product drops, whichresults in further increase of the cost of the device. It is difficultto spread this expensive device as a general-purpose component for amobile communication apparatus. Since the liquid etching reagent for usein removing sacrificial materials such as phosphor silicate glass (PSG)corrodes the layers of the lower electrode, the piezoelectric thin film,and the upper electrode constituting the upper structure, the materialsusable in the upper structure are remarkably limited, Furthermore, thereis a serious problem that it is difficult to prepare an FBAR or SBARstructure having a desired dimensional precision.

As piezoelectric materials for the thin film piezoelectric device,aluminum nitride (AlN), zinc oxide (ZnO), cadmium sulfide (CdS), leadtitanate (PT(PbTiO₃)), lead zirconate titanate (PZT(Pb(Zr, Ti)O₃)) andthe like are used. Especially, AlN has a high propagation speed of anelastic wave, and is suitable as the piezoelectric material for a thinfilm piezoelectric resonator and a thin film filter operating in ahigh-frequency band region.

Since the FBAR and SRAR obtain resonance by propagation of the elasticwave in the thin film, resonance characteristics of the FBAR and SBARare largely influenced by not only vibration characteristics of thepiezoelectric thin film but also those of the electrode layer or thesubstrate film. Therefore, various restrictions exist from a vibrationcharacteristic aspect with respect to shapes and thicknesses of theelectrode layer and the substrate film. For example, when the electrodelayer or the substrate film is thickened, there is a problem thateffective electromechanical coupling coefficient of the FBAR or SBAR isreduced. On the other hand, when the metal electrode layer is thinnedand elongated, conductor loss becomes higher by the increase of electricresistance, and therefore various restrictions are generated indesigning the structure of the thin film piezo electric device preparedby combining a plurality of FBARs or SBARs.

The thin film piezoelectric device exerting a sufficient performance ina gigahertz band has not been obtained for the above reason. Therefore,there has been a strong demand for realization of a high-performancethin film piezoelectric device in which all characteristics such as anelectromechanical coupling coefficient, acoustic quality factor (Qvalue), temperature stability of a resonant frequency, and insertionloss of a vibration portion including not only the piezoelectric thinfilm but also the electrode layer and the substrate film are improved.Especially, the insertion loss is an important parameter whichinfluences the performance in constituting the resonator or the filter,and largely depends on the quality and characteristics of the metalelectrode thin film for use.

DISCLOSURE OF THE INVENTION

The present invention has been developed in consideration of theabove-described problems, and an object of the present invention is toprovide a thin film piezoelectric device which is prepared by combininga plurality of resonators constituted of an FBAR or an SBAR having alarge electromechanical coupling coefficient and superior acousticquality factor (Q value) and frequency temperature characteristic andwhose insertion loss is small and whose performance has been improved.

According to the present invention, to achieve the above-describedobject, there are provided the following high-performance thin filmpiezoelectric device which is superior in the acoustic quality factor,bandwidth, temperature characteristic and the like and whose insertionloss is small, and a method of manufacturing the device.

It has been known that the insertion loss of the thin film piezoelectricdevice, for example, a filter prepared by combining a plurality of thinfilm piezoelectric resonators depends on a conductor loss of a metalelectrode layer. The present inventors have considered that electricresistance of a metal electrode electrically connected to adjacent thinfilm piezoelectric resonators drops, when a distance between centers ofthe adjacent thin film piezoelectric resonators is shortened, and, as aresult, the insertion loss can be largely lowered. Then, as a result ofvarious studies of measures to shorten the distance between the centersof the adjacent thin film piezoelectric resonators, it has been foundthat applying of anisotropic etching by a deep graving type reactive ionetching (deep RIE) process which is deep trench etching utilizing plasmais most preferable solving means both in improvement of the performanceof the thin film piezoelectric device and reduction of the cost.

In order to attain the above object, according to the present invention,there is provided a thin film piezoelectric device including a substratehaving a plurality of vibration spaces and a piezoelectric laminatedstructure formed on the substrate, a plurality of thin filmpiezoelectric resonators being formed facing the vibration spaces,

wherein the piezoelectric laminated structure has at least apiezoelectric film and a metal electrode formed on at least a part ofeach of opposite surfaces of the piezoelectric film,

the piezoelectric laminated structure comprises diaphragms positionedfacing the vibration spaces, and a support area other than thediaphragms,

at least one set of two adjacent thin film piezoelectric resonators areelectrically connected to each other through the metal electrode,

the thin film piezoelectric device comprising at least one set of twoadjacent thin film piezoelectric resonators in which D0 is a distancebetween the centers of the diaphragms of the two electrically connectedadjacent thin film piezoelectric resonators and D1 is a length of asegment of a support area on a straight line passing through centers ofthe diaphragms of two electrically connected adjacent thin filmpiezoelectric resonators, and a ratio D1/D0 is 0.1 to 0.5.

In an aspect of the present invention, the ratio D1/D0 is in a range of0.1 to 0.5 with respect to all the sets of two electrically connectedadjacent thin film piezoelectric resonators. In an aspect of the presentinvention, each of the vibration spaces is fabricated by a via holeextending from the surface of the substrate on which the piezoelectriclaminated structure is formed to the opposite surface, and a side wallsurface of the via hole forms an angle in a range of 80 to 100° withrespect to the surface of the substrate on which the piezoelectriclaminated structure is formed.

In an aspect of the present invention, the piezoelectric laminatedstructure comprises a lower electrode constituting the metal electrode,the piezoelectric film, and an upper electrode constituting the metalelectrode stacked in order from the substrate side in at least one thinfilm piezoelectric resonator. In an aspect of the present invention, theupper electrode of the at least one thin film piezoelectric resonatorcomprises two electrode portions.

In an aspect of the present invention, the piezoelectric laminatedstructure comprises a lower electrode constituting the metal electrode,a first piezoelectric film, an inner electrode constituting the metalelectrode, a second piezoelectric film, and an upper electrodeconstituting the metal electrode stacked in order from the substrateside in at least one thin film piezoelectric resonator.

In an aspect of the present invention, at least one insulating layer ofsilicon oxide and/or silicon nitride as a main component is attached tothe diaphragm. In an aspect of the present invention, an insulatinglayer comprising at least one layer of silicon oxide and/or siliconnitride as a main component intervenes only between the support area ofthe piezoelectric laminated structure and the substrate.

In an aspect of the present invention, the piezoelectric film is anoriented crystal film represented by a general formula Al_(1-x)Ga_(x)N(where 0<x<1) and made of a solid solution of aluminum nitride andgallium nitride showing a c-axis orientation, and a rocking curve halfvalue width (FWHM) of a diffraction peak of a (0002) surface of the filmis 3.0° or less in at least one thin film piezoelectric resonator. In anaspect of the present invention, the piezoelectric film is a zinc oxidethin film showing a c-axis orientation, and a rocking curve half valuewidth (FWHM) of a diffraction peak of a (0002) surface of the film is3.0° or less in at least one thin film piezoelectric resonator. In anaspect of the present invention, the piezoelectric film is a leadtitanate thin film or a lead zirconate titanate thin film in at leastone thin film piezoelectric resonator.

In an aspect of the present invention, the planar shape of one of thediaphragms has two pairs of opposite sides, and at least one part ofopposite sides is formed to be non-parallel in at least one thin filmpiezoelectric resonator. In an aspect of the present invention, at leasta part of the planar shape of one of the diaphragms is formed by anon-square irregular polygonal shape in at least one thin filmpiezoelectric resonator. In an aspect of the present invention, theplanar shape of one of the diaphragms is formed by a non-squareirregular polygonal shape including a curved portion in at least a partof the shape in at least one thin film piezoelectric resonator.

In an aspect of the present invention, the thin film piezoelectricdevice being a thin film piezoelectric filter. In an aspect of thepresent invention, the thin film piezoelectric filter comprises, aladder type circuit comprising a plurality of thin film piezoelectricresonators connected in series and at least one of the thin filmpiezoelectric resonators branched from/connected to the plurality ofresonators connected in series.

In an aspect of the present invention, the thin film piezoelectricdevice being a duplexer comprising a plurality of thin filmpiezoelectric filters. In an aspect of the present invention, the thinfilm piezoelectric filter comprises a ladder type circuit comprising aplurality of thin film piezoelectric resonators connected in series andat least one of the thin film piezoelectric resonators branchedfrom/connected to the plurality of resonators connected in series.

In order to attain the above object, according to the present invention,there is also provided a method of manufacturing the thin filmpiezoelectric device according to claim 1, comprising the steps of:forming the piezoelectric laminated structure on the substratecomprising a semiconductor or an insulator; and thereafter forming thevibration spaces in the substrate from a side opposite to the side onwhich the piezoelectric laminated structure is fabricated by a deepgraving type reactive ion etching process.

In order to attain the above object, according to the present invention,there is also provided a thin film piezoelectric resonator formed usinga substrate having a vibration space, and a piezoelectric laminatedstructure formed on the substrate, wherein the piezoelectric laminatedstructure comprises at least a piezoelectric film and a metal electrodeformed on at least a part of each of the fabricated by a via holeextending from the surface of the substrate on which the piezoelectriclaminated structure is formed to an opposite surface, and a side wallsurface of the via hole forms an angle in a range of 80 to 100° withrespect to the surface of the substrate on which the piezoelectriclaminated structure is formed.

In the present invention, to form the vibration portion having astructure in which the layer of the piezoelectric material is heldbetween the plurality of metal electrodes on the upper surface of thesubstrate constituted of the semiconductor or the insulator, thesubstrate portion present under the portion constituting the vibrationportion is anisotropically removed from the underside of the substrateby the deep graving type reactive ion etching (deep RIE) process whichis deep trench etching utilizing plasma, and the via hole constitutingthe vibration space is formed. It is to be noted that in the presentdescription, the main surface which is one of two main surfaces of thesubstrate and on which the piezoelectric laminated structure includingthe vibration portion is formed is referred to as the “upper surface”for the sake of convenience, and the other main surface is sometimesreferred to as the “lower surface” for the sake of convenienece.

The deep RIE process is plasma etching using a reactive gas, and issuitable for anisotropically working the silicon wafer at a high etchingspeed to form a deep trench or via hole having a substantially verticalsectional shape at a tapered angle close to verticality. One examplewill be described. The silicon wafer in which the predetermined portionis masked with a pattern formed by photo resist is charged in thereaction vessel of the dry etching equipment comprising an inductivelycoupled plasma generation power supply. The silicon wafer is clamped ona high-frequency (13.56 MHz) electrode by an electrostatic chuck, andheld in the vicinity of room temperature (−20 to 60° C.) by cooling witha helium gas. While a plasma state is held to be constant, the etchingof silicon and the formation of the protective film on the side wall canbe alternately, and periodically performed by adoption of a timemodulation process in which an SF₆ gas that is an etching gas and a C₄F₈gas for forming the protective film are alternately introduced into thevessel by a gas switch control unit. At the C₄F₈ discharge time in thefirst step, the protective film is formed on the side wall by depositionof an nCF₂ polymer based film by ionization and dissociation of the C₄F₈gas.

In the second step, the high-frequency bias potential is applied, andthe protective film on the bottom surface of a working pattern isefficiently removed. The etching in a vertical direction proceeds bycollision of fluorine radicals generated by the SF₆ discharge of thethird step. When the time constant of each step is optimized, depositionof necessary minimum amount of protective film and high-anisotropyetching by the SF₆ plasma can be realized. The etching speed, etchingworked shapes selection ratio of silicon to the mask material,uniformity of the etching and the like are influenced by the timeconstant of each step. This method has a characteristic that any specialequipment for controlling the sample temperature is not required, andthe working at the high etching speed and with high anisotropy can beperformed in the vicinity of room temperature.

That is, the side wall of the via hole is formed at the tapered angleclose to the verticality toward the upper surface from the lower surfaceof the substrate by the application of the deep RIE process. Therefore,a via hole having a small difference between the dimension of thediaphragm which corresponds to a portion of the lower electrode or theinsulating layer facing via hole which is a vibration space and that ofthe opening in the lower surface of the substrate is formed, and thedistance between the centers of the electrically connected adjacent thinfilm piezoelectric resonators can be shortened. Here, the tapered angleis an angle formed by the average plane representing the side wallsurface of the via hole formed toward the upper surface from the lowersurface of the substrate with the lower surface of the substrate or theupper surface of the substrate. When the tapered angle or club-shapedangle is in a range of 80 to 100 degrees, it can be said that the angleis close to verticality. A plurality of thin film piezoelectricresonators are constituted and formed into a device in such a mannerthat, on a straight line connected to the centers (two-dimensionalgeometric gravity centers) in the surfaces parallel to the uppersurfaces of the substrate of the electrically connected adjacent thinfilm piezoelectric resonators, the ratio D1/D0 of the length D1 of thesegment passing through the support area of the piezoelectric laminatedstructure existing between the diaphragms of the adjacent thin filmpiezoelectric resonators to the distance D0 between the centers of theelectrically connected adjacent thin film piezoelectric resonators is0.1 to 0.5. The arrangement in which the above-described ratio D1/D0 is0.1 to 0.5 is preferable in all combinations of the electricallyconnected adjacent thin film piezoelectric resonators, and thisarrangement may be applied to at least one set of adjacent thin filmpiezoelectric resonators. When the plurality of thin film piezoelectricresonators integrated in this manner are combined, a thin filmpiezoelectric device can be manufactured having a small insertion lossand excellent characteristic and high performance.

The center (two-dimensional geometric gravity center) in the surfaceparallel to the upper surface of the substrate of the thin filmpiezoelectric resonator in the present invention is the two-dimensionalcenter of the diaphragm constituting the thin film piezoelectricresonator, and means the two-dimensional geometric gravity center of thediaphragm. The two-dimensional geometric gravity center of the shapesurrounded with arbitrary closed curve can be obtained, when the balanceis actually measured in two cases of different gravity directions, andmay be graphically obtained. For example, as to the quadrangle, asdescribed in “Introduction to Geometry” by Coxeter, “when eight pointseach dividing each side of the quadrangle into three equal parts aretaken, and new quadrangle surrounded by four straight lines each passingthrough two points each dividing the side of the original quadrangleinto three equal parts, and existing adjacent to each vertex of theoriginal quadrangle, is made, this new quadrangle is a parallelogram”.At this time, the intersection of the diagonal lines of theparallelogram is a geometric gravity center. In the case of an n-gonshape (n is an integer of 4 or more), the diagonal line is drawn usingone vertex of the n-gon shape as a starting point, and the shape isdivided into n-2 triangles. When the weighted average of the gravitycenter of each of the divided triangles is obtained, the gravity centerof the whole n-gon shape is obtained.

The piezoelectric laminated structure constituting the thin filmpiezoelectric resonator in the present invention is formed of two areasdefined by the positional relation with respect to the substrate havinga vibration space. One area is the diaphragm positioned above thevibration space, and the other area is the support area positioned onthe substrate portion (support portion), excluding the vibration space.

In the present invention, the straight line (present in the surfaceparallel to the upper surface of the substrate) connecting thetwo-dimensional centers of the electrically connected adjacent thin filmpiezoelectric resonators to each other, that is, the two-dimensionalcenters of the diaphragms of the electrically connected adjacent thinfilm piezoelectric resonators passes through the respective diaphragmsof the adjacent thin film piezoelectric resonators and the support areaexisting between two diaphragms. Assuming that the lengths of thesegments of the straight line passing through the diaphragms of theadjacent thin film piezoelectric resonators are D2, D3, and the lengthof the segment passing through the support area is D1, the distance D0between the centers of the adjacent thin film piezoelectric resonatorsis represented by:D0=D1+D2+D3.

In the present invention, each thin film piezoelectric resonator isdisposed in a position wherein the straight line connecting thetwo-dimensional centers (centers of the diaphragms) of the electricallyconnected adjacent thin film piezoelectric resonators to each, other hasthe length D1 of the segment passing through the support area existingbetween the adjacent thin film piezoelectric resonators and the distanceD0 between the centers of the adjacent thin film piezoelectricresonators, and the ratio D1/D0 is 0.1 to 0.5, preferably 0.18 to 0.3.When the ratio D1/D0 is smaller than 0.1, the substrate portion (i.e.,the side wall portion) between two via holes constituting the adjacentthin film piezoelectric resonators becomes thin, the strength remarkablydrops, add the handling becomes difficult. For example, the portionunfavorably breaks during working such as dicing or during deviceassembly. The side wall portion between the adjacent via holes performsa function of supporting the piezoelectric laminated structure includingthe piezoelectric film formed on the upper surface of the substrate.When the ratio D1/D0 exceeds 0.5, the distance between the centers ofthe electrically connected adjacent thin film piezoelectric resonatorsexcessively broadens, the dimension (length) of the metal electrodeconnecting both the resonators to each other increases, and the electricresistance of the metal electrode excessively increases. When theelectric resistance of the metal electrode increases, the insertion lossof the assembled thin film piezoelectric device increases, and thedevice cannot be practically used as a high-frequency circuit componentsuch as a filter for a communication apparatus.

In the present invention, D1 is, for example, 25 to 70 μm, preferably 30to 60 μm, and D0 is, for example, 100 to 300 μm, preferably 150 to 250μm. When these dimensions are excessively small, the substrate portion(i.e., the side wall portion) between two via holes constituting theadjacent thin film piezoelectric resonators becomes thin, the strengthremarkably drops, and the handling becomes difficult. On the other hand,when the dimensions are excessively large, the distance between thecenters of the electrically connected adjacent thin film piezoelectricresonators excessively broadens, the dimension (length) of the metalelectrode connecting both the resonators to each other increases, andthe electric resistance of the metal electrode excessively increases.

Moreover, according to the present invention, in the thin filmpiezoelectric resonator constituted in the position where the ratioD1/D0 of the length D1 of the segment passing through the support areain which the straight line exists between the diaphragms of theelectrically connected adjacent thin film piezoelectric resonators tothe distance D0 between the centers of the adjacent thin filmpiezoelectric resonators is 0.1 to 0.5, the planar shape of thediaphragm constituting the vibration portion of the thin filmpiezoelectric resonator is devised and optimized. Accordingly, the thinfilm piezoelectric device can be manufactured in which any extraspurious signal or noise does not enter a pass band and which has a lowinsertion loss and high characteristic and performance. Concreteexamples of the preferable planar shape of the diaphragm include: ashape (quadrangle) having two pairs of opposite sides in such a mannerthat at least one pair of opposite sides are formed to be non-parallel;a polygonal shape including a non-square irregular polygonal shape in atleast a part of the shape; a non-square irregular polygonal shapeincluding a curved portion in at least a part of the shape and the like.When the symmetry of the planar shape of the diaphragm is lowered, anyextra spurious signal or noise cannot enter the desired pass band, andthe performance of the thin film piezoelectric device for use as thehigh-frequency circuit component is enhanced.

The thin film piezoelectric device of the present invention has asubstrate having a plurality of vibration spaces, and a piezoelectriclaminated structure formed on the substrate, and a plurality of thinfilm piezoelectric resonators are formed using the substrate. In oneembodiment of the thin film piezoelectric resonator, a lower electrode,a piezoelectric film, and an upper electrode are formed on the substratehaving a plurality of vibration spaces. The upper electrode may comprisetwo electrode portions.

Moreover, in another embodiment of the thin film piezoelectric resonatorconstituting the thin film piezoelectric device of the presentinvention, the piezoelectric laminated structure comprises a lowerelectrode, a piezoelectric film, an inner electrode, a piezoelectricfilm, and an upper electrode stacked in order from the substrate side.

In the present invention, as the piezoelectric material for the thinfilm piezoelectric device, aluminum nitride (AlN), aluminumnitride-gallium nitride based solid solution (Al_(1-x)Ga_(x)N), zincoxide (ZnO), lead titanate (PbTiO₃), lead zirconate titanate (PZT(Pb(Zr,Ti)O₃)) and the like are usable. Especially, AlN has a high propagationspeed of an elastic wave, and is suitable as the piezoelectric materialfor a thin film piezoelectric resonator and a thin film filter operatingin a high-frequency band region.

To utilize the above-described features of the piezoelectric thin film,and improve the temperature stability of resonant frequency, it iseffective to form a silicon oxide (SiO₂) layer as an insulating layer inthe vibration portion. The vibration portion means a region in which atleast two electrodes holding the piezoelectric film therebetween aresuperimposed in the diaphragm. SiO₂ has a positive temperaturecoefficient, and is capable of compensating for the temperature changeof the resonant frequency of the piezoelectric material having anegative temperature coefficient. The insulating layer may be an SiO₂single layer, or a composite layer containing SiO₂ and silicon nitride(Si₃N₄ or SiN_(x)) as a main component, As the insulating layer, anSi₃N₄ single layer or an SiN_(x) single layer is usable. Furthermore, itis possible to use AlN for use as the material of the piezoelectriclayer and as the material of the insulating layer.

Here, to realize the superior resonance characteristics of the thin filmpiezoelectric resonator, the thickness of the insulating layer ispreferably set to a special range. For example, assuming that thethickness of the piezoelectric thin film containing AlN as the maincomponent is t, and the thickness of the whole insulating layercontaining silicon oxide as the main component is t′, the effect isespecially remarkable in a range satisfying 0.1≦t′/t≦0.5, and theelectromechanical coupling coefficient, the acoustic quality factor, andthe temperature stability of the resonant frequency are all remarkablysatisfactory. When t′/t<0.1, the electromechanical coupling coefficientand the acoustic quality factor tends to be enhanced, but the effect ofimproving the temperature characteristic of the resonant frequency isreduced. When t′/t>0.5, the electromechanical coupling coefficient andthe acoustic quality factor are impaired by the presence of theinsulating layer. When the insulating layer is an SiO₂ layer, thepiezoelectric thin film made of a material other than AlN is preferablyused because the absolute value of the temperature coefficient of theresonant frequency is reduced, and the characteristic of the FBAR issatisfactory.

In the thin film piezoelectric resonator constituting the thin filmpiezoelectric device of the present invention, for a purpose ofimproving the temperature characteristic of the resonant frequency, asdescribed above, the insulating layer containing SiO₂ and/or siliconnitride (Si₃N₄ or SiN_(x)) as the main component can be formed in thevibration portion. On the other hand, when the piezoelectric materialhaving the satisfactory temperature stability of the resonant frequencyis used, it is possible to eliminate all the insulating layers. That is,a constitution may be adopted in which the insulating layer containingSiO₂ as the main component exists only between the support area of thepiezoelectric laminated structure and the support portion of thesubstrate, and the insulating layer does not exist in the diaphragmportion which is the vibration portion.

The piezoelectric thin film made of aluminum nitride-gallium nitridebased solid solution (Al_(1-x)Ga_(x)N) or zinc oxide (ZnO) for use asthe piezoelectric materials for the thin film piezoelectric deviceindicates c-axis orientation, and a rocking curve half value width(FWHM) of a diffraction peak of a (0002) surface measured by an X-raydiffraction method is preferably 3.0° or less. When the rocking curvehalf value width (FWHM) exceeds 3.0°, an electromechanical couplingcoefficient K_(t) ² drops, the pass bandwidth necessary for forming thedevice cannot be sufficiently taken, and the resonance characteristic issometimes deteriorated.

As to lead titanate (PT(PbTiO₃)) and lead zirconate titanate (PZT(Pb(Zr,Ti)O₃), there is little dependence of the device characteristic on therocking curve half value width (FWHM) indicating orientation of crystal.

As described above, when the distance between the centers of theelectrically connected adjacent thin film piezoelectric resonators isshortened, the planar shape of the diaphragm is preferably optimized,and a plurality of thin film piezoelectric resonators havingsatisfactory resonance characteristic are combined and integrated, theinsertion loss caused by the conductor loss of the metal electrode canbe remarkably reduced. The high-performance thin film piezoelectricdevice can be realized in which the electromechanical couplingcoefficient (e.g., the electromechanical coupling coefficient K_(t) ²obtained from the measured values of the resonant frequency andantiresonant frequency in a range of 2.0 to 3.0 GHz is more than 4.0%)and the acoustic quality factor (Q value) are large and whose insertionloss is small and which is superior in gain and band characteristic. Thehigh-performance thin film piezoelectric device is usable as variousdevices for a mobile communication apparatus. In the thinfilm-piezoelectric resonator of the present invention, since thevibration space is formed at the tapered angle or club-shaped angleclose to verticality toward the upper surface from the lower surface ofthe substrate by the deep graving type reactive ion etching (deep RIE)process, the thin film piezoelectric resonators can be disposed in thevicinity of each other, and the above-described high-performance devicecan be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic plan view showing one embodiment of a thin filmpiezoelectric device according to the present invention;

FIG. 1B is a schematic sectional view along an X-X′ line of FIG. 1A;

FIG. 1C is a schematic sectional view along a Y-Y′ line of FIG. 1A;

FIG. 2A is a schematic plan view showing another embodiment of the thinfilm piezoelectric device according to the present invention;

FIG. 2B is a schematic sectional view along an X-X′ line of FIG. 2A;

FIG. 2C is a schemtic sectional view along a Y-Y′ line of FIG. 2A;

FIG. 3A is a schematic plan view showing still another embodiment of thethin film piezoelectric device according to the present invention;

FIG. 3B is a schematic sectional view along an X-X′ line of FIG. 3A;

FIG. 4A is a schematic plan view showing still another embodiment of thethin film piezoelectric device according to the present invention;

FIG. 4B is an explanatory diagram of a distance between centers ofadjacent diaphragms in FIG. 4A;

FIG. 5A is a schematic plan view showing still another embodiment of thethin film piezoelectric device according to the present invention;

FIG. 5B is an explanatory diagram of the distance between the centers ofthe adjacent diaphragms in FIG. 5A;

FIG. 6A is a graph showing an impedance frequency characteristic of thethin film piezoelectric device of Example 6;

FIG. 6B is a graph showing a filter pass band characteristic of the thinfilm piezoelectric device of Example 6;

FIG. 7A is a graph showing an impedance frequency characteristic of thethin film piezoelectric device of Example 13;

FIG. 7B is a graph showing the filter pass band characteristic of thethin film piezoelectric device of Example 13;

FIG. 8A is a schematic plan view showing one reference example of thethin film piezoelectric device;

FIG. 8B is a schematic sectional view along an X-X′ line of FIG. 8A;

FIG. 9 is a schematic sectional plan view showing still anotherembodiment of the thin film piezoelectric device according to thepresent invention; and

FIG. 10 is a block diagram showing a constitution of a duplexeraccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of a thin film piezoelectric resonator, a thin filmpiezoelectric device, and a method of manufacturing the device will bedescribed hereinafter in detail with reference to the drawings.

First, a thin film piezoelectric device for reference will be describedbefore description of the embodiments of the present invention.

FIG. 8A is a schematic plan view showing one reference example of thethin film piezoelectric device, and FIG. 8B is an X-X′ schematicsectional view. In these figures, a thin film piezoelectric device 100is prepared by combining an FBAR 110, an FBAR 120, an FBAR 130, and anFBAR 140. The FBAR 120 has a substrate 12, an insulating layer 13 formedon the upper surface of the substrate 12, and a piezoelectric laminatedstructure 14 prepared on the upper surface of the insulating layer 13.The piezoelectric laminated structure 14 comprises a lower electrode 15formed on the upper surface of the insulating layer 13, a piezoelectricfilm 16 formed on the upper surface of the insulating layer 13 which isa substrate film in such a manner as to coat the lower electrode 15, andan upper electrode 17 formed on the upper surface of the piezoelectricfilm 16. The substrate 12 is provided with via holes 22 forming gaps. Apart of the insulating layer 13 is exposed toward the via hole 22. Anexposed portion of the insulating layer 13 and a portion of thepiezoelectric laminated structure 14 existing in a correspondingposition constitute a diaphragm 23 forming a vibration portion. Thelower electrode 15 and the upper electrode 17 have main body portions 15a, 17 a formed in an area corresponding to the diaphragm 23, andterminal portions 15 b, 17 b for connection of the main body portions 15a, 17 a to the other FBAR or an external circuit. The terminal portions15 b, 17 b extend to the outside of the area corresponding to thediaphragm 23. The FBAR 110, FBAR 130, and FBAR 140 are also similarlyconstituted.

In this reference example, for example, when the substrate 12 is made ofsilicon, a part of the silicon substrate is etched and removed from thelower surface using a heated KOH aqueous solution to thereby form thevia holes 22. However, when wet etching is performed using alkali suchas KOH, the etching proceeds at a tilt of 54.7 degrees with respect to a(100) silicon substrate surface because the etching proceeds in parallelwith a (111) surface, and a distance between the diaphragms of theadjacent resonators becomes remarkably large, For example, the diaphragm23 having a planar dimension of 150 μm×150 μm, constituted on the uppersurface of a silicon wafer with a thickness of 300 μm, requires a lowersurface side etching opening 24 of about 575 μm×575 μm, and a distancebetween the diaphragm centers of the adjacent resonators is 575 μm ormore. That is, a dimension of the support area of the piezoelectriclaminated structure existing between electrically connected adjacentthin film piezoelectric resonators is a long distance of about 0.74times or more the distance between the centers of the diaphragms of theadjacent thin film piezoelectric resonators.

Therefore, high-density integration of the FBAR resonator is hindered.Moreover, when the adjacent resonators are electrically connected toeach other by metal electrodes (lower electrode 15 and upper electrode17) holding the piezoelectric film 16 therebetween, electric resistanceof the metal electrode increases. Therefore, there is caused a problemthat insertion loss of the thin film piezoelectric device 100 preparedby combining the FBAR resonators 110, 120, 130, and 140 is remarkablylarge.

On the other hand, one embodiment of a thin film piezoelectric deviceaccording to the present invention has a constitution shown in FIGS. 1Ato 1C. FIG. 1A is a schematic plan view showing the thin filmpiezoelectric device of the present embodiment, FIG. 1B is an X-X′schematic sectional view, and FIG. 1C is a Y-Y′ schematic sectionalview. In these figures, a thin film piezoelectric device 200 is preparedby combining an FBAR 210, an FBAR 220, an FBAR 230, and an FBAR 240. TheFBAR 220 has a substrate 12, an insulating layer 13 formed on the uppersurface of the substrate 12, and a piezoelectric laminated structure 14prepared on the upper surface of the insulating layer 13. Thepiezoelectric laminated structure 14 comprises a lower electrode 15formed on the upper surface of the insulating layer 13, a piezoelectricfilm 16 formed on the upper surface of the insulating layer 13 in such amanner as to coat the lower electrode 15, and an upper electrode 17formed on the upper surface of the piezoelectric film 16. The substrate12 is provided with via holes 22 forming gaps. A part of the insulatinglayer 13 is exposed toward the via hole 22. An exposed portion of theinsulating layer 13 and a portion of the piezoelectric laminatedstructure 14 existing in a corresponding position constitute a diaphragm23 including a vibration portion. The lower electrode 15 and the upperelectrode 17 have main body portions 15 a, 17 a formed in an areacorresponding to the diaphragm 23, and terminal portions 15 b, 17 b forconnection of the main body portions 15 a, 17 a to the other FBAR or anexternal circuit. The terminal portions 15 b, 17 b extend to the outsideof the area corresponding to the diaphragm 23. The FBAR 210, FBAR 230,and FBAR 240 are also similarly constituted.

In the present embodiment, by application of a deep RIE process, theside wall surface of the via hole 22 is formed from one surface (e.g.,the lower surface) of the substrate 12 to the opposite surface (e.g.,the upper surface) at a tapered angle or club-shaped angle close toverticality. Thus, the via hole 22 is formed with a small differencebetween the dimension of the diaphragm 23 which corresponds to a portionof the lower electrode 15 or the insulating layer 13 facing the via hole22 constituting a vibration space and that of an etching opening 24 of alower surface of the substrate, and therefore adjacent thin filmpiezoelectric resonators can be brought close to each other anddisposed. Therefore, in a straight line (X-X′ line in FIG. 1A) passingthrough centers (two-dimensional geometric gravity centers) 1 and 2 in aplane parallel to the substrate surfaces of the diaphragms 23 of theelectrically connected adjacent thin film piezoelectric resonators 210and 220, a ratio D1/D0 can be reduced where D1 is a length of a segmentpassing through the support area of the piezoelectric laminatedstructure on the straight line existing between the adjacent thin filmpiezoelectric resonators and D0 is a distance between the diaphragmcenters of the adjacent thin film piezoelectric resonators (see FIGS. 1Aand 1B). The thin film piezoelectric resonators 210, 220 areelectrically connected to each other via the lower electrode 15. Theelectrically connected adjacent thin film piezoelectric resonators 210and 230 also have a similar relation. The electrically connectedadjacent thin film piezoelectric resonators 220 and 240 also have asimilar relation, and in this case, the electric connection is performedvia the upper electrode 17.

The thin film piezoelectric device of the present embodiment is a thinfilm piezoelectric filter constituted by a ladder type circuit in whichthe thin film piezoelectric resonator 210 is connected in series to thethin film piezoelectric resonator 220, and the thin film piezoelectricresonators 230 and 240 are branched/connected to the resonators 210,220, respectively.

FIGS. 2A to 2C show another embodiment of the thin film piezoelectricdevice according to the present invention. FIG. 2A is a schematic planview showing the thin film piezoelectric device of the presentembodiment, FIG. 2B is an X-X′ schematic sectional view, and FIG. 2C isa Y-Y′ schematic sectional view. In these figures, members havingfunctions similar to those in FIGS. 1A to 1C described above are denotedwith the same reference numerals.

A thin film piezoelectric device 200 is prepared by combining an FBAR210, an FBAR 220, an FBAR 230, and an FBAR 240. The FBAR 220 has asubstrate 12 provided with via holes 22 forming gaps, and apiezoelectric laminated structure 14 prepared on the upper surface ofthe insulating layer 13 in such a manner as to be bridged across the viahole 22. In the present embodiment, the insulating layer 13 exists inportions (support portions for the piezoelectric laminated structure 14)other than the via holes 22 in the upper surface of the substrate 12,and the insulating layer 13 intervenes between the support area of thepiezoelectric laminated structure 14 and the support portion of thesubstrate.

Since the insulating layer 13 does not exist in the portion of thediaphragm 23 facing the via hole 22, an electromechanical couplingcoefficient increases, and a bandwidth broadens. The piezoelectriclaminated structure 14 comprises a lower electrode 15 a part of whichcontacts the upper surface of the insulating layer 13, a piezoelectricfilm 16 formed on the upper surface of the insulating layer 13 in such amanner as to coat the lower electrode 15, and an upper electrode 17formed on the upper surface of the piezoelectric film 16. A part of thelower electrode 15 is exposed toward the via hole 22 without disposingthe insulating layer 13. An exposed portion of the lower electrode 15and a portion of the piezoelectric laminated structure 14 existing in acorresponding position constitute a diaphragm 23 including a vibrationportion. The lower electrode 15 and the upper electrode 17 have mainbody portions 15 a, 17 a formed in an area corresponding to thediaphragm 23, and terminal portions 15 b, 17 b for connection of themain body portions 15 a, 17 a to the other FBAR or an external circuit.The terminal portions 15 b, 17 b extend to the outside of the areacorresponding to the diaphragm 23. The FBAR 210, FBAR 230, and FBAR 240are also similarly constituted.

Also in the present embodiment, in the same manner as in the embodimentof FIGS. 1A to 1C, the adjacent thin film piezoelectric resonators canbe brought close to each other and disposed. Therefore, in a straightline (X-X′ line in FIG. 2A) passing through centers (two-dimensionalgeometric gravity centers) 1 and 2 of the diaphragms 23 of theelectrically connected adjacent thin film piezoelectric resonators 210and 220, a ratio D1/D0 can be reduced, where D1 is a length of a segmentpassing through the support area of the piezoelectric laminatedstructure on the straight line existing between the diaphragms 23 of theadjacent thin film piezoelectric resonators and D0 is a distance betweenthe diaphragm centers of the adjacent thin film piezoelectric resonators(see FIGS. 2A and 2B). The thin film piezoelectric resonators 210, 220are electrically connected to each other via the lower electrode 15. Theelectrically connected adjacent thin film piezoelectric resonators 210and 230 also have a similar relation. The electrically connectedadjacent thin film piezoelectric resonators 220, and 240 also have asimilar relation, and in this case, the electric connection is performedvia the upper electrode 17.

The thin film piezoelectric device of the present embodiment is a thinfilm piezoelectric filter constituted by a ladder type circuit in whichthe thin film piezoelectric resonator 210 is connected in series to thethin film piezoelectric resonator 220, and the thin film piezoelectricresonators 230 and 240 are branched/connected to the resonators 210,220, respectively.

FIGS. 3A and 3B show still another embodiment of the thin filmpiezoelectric device according to the present invention. FIG. 3A is aschematic plan view showing the thin film piezoelectric device of thepresent embodiment, and FIG. 3B is an X-X′ schematic sectional view.Also in these figures, members having functions similar to those inFIGS. 1A to 2C described above are denoted with the same referencenumerals.

A thin film piezoelectric device 200 is prepared by combining an FBAR210, an FBAR 220, an FBAR 230, an FBAR 240, and an FBAR 250. The FBAR220 has a substrate 12, an insulating layer 13 formed on the uppersurface of the substrate 12, and a piezoelectric laminated structure 14prepared on the upper surface of the insulating layer 13. Thepiezoelectric laminated structure 14 comprises a lower electrode 15formed on the upper surface of the insulating layer 13, a piezoelectricfilm 16 formed on the upper surface of the insulating layer 13 in such amanner as to coat the lower electrode 15, and an upper electrode 17formed on the upper surface of the piezoelectric film 16. The substrate12 is provided with via holes 22 forming gaps. A part of the insulatinglayer 13 is exposed toward the via hole 22. An exposed portion of theinsulating layer 13 and a portion of the piezoelectric laminatedstructure 14 existing in a corresponding position constitute a diaphragm23 including a vibration portion. The lower electrode 15 has a main bodyportion 15 a formed in an area corresponding to the diaphragm 23, and aterminal portion 15 b for connection to the other FBAR or an externalcircuit. The terminal portion 15 b extends to the outside of the areacorresponding to the diaphragm 23. In the present embodiment, the upperelectrode 17 has a first electrode portion 17A and a second electrodeportion 17B. These electrode portions 17A, 17B have main body portions17Aa, 17Ba, and terminal portions 17Ab, 17Bb. The main body portions17Aa, 17Ba are positioned in the area corresponding to the diaphragm 23,and the terminal portions 17Ab, 17Bb for the connection of the main bodyportions 17Aa, 17Ba to the other FBAR or the external circuit extend tothe outside of the area corresponding to the diaphragm 23.

The FBAR 220 comprising the upper electrode including two electrodeportions shown in the embodiment of FIGS. 3A and 3B is referred to as amultiplex mode resonator. An input voltage is applied between oneelectrode portion (e.g., the second electrode portion 17B) of the upperelectrode 17 and the lower electrode 15, and the voltage between theother electrode portion (e.g., the first electrode portion 17A) of theupper electrode 17 and the lower electrode 15 can propagate as an outputvoltage to the adjacent FBAR 210. Therefore, the FBAR 220 itselfdevelops the function of a filter. When the filter having thisconstitution is used as a constituting element of a band pass filter, awire-bonding in an element can be omitted, therefore there is not anyloss caused by the wire-bonding, attenuation characteristic of ablocking band becomes satisfactory, and frequency response is enhanced.This also applies to the FBAR 210.

Also in the present embodiment, in the same manner as in the embodimentof FIGS. 1A to 1C, the adjacent thin film piezoelectric resonators canbe brought close to each other and disposed. Therefore, in a straightline (X-X′ line in FIG. 3A) passing through centers (two-dimensionalgeometric gravity centers) 1 and 2 of the diaphragms 23 of theelectrically connected adjacent thin film piezoelectric resonators 210and 220, a ratio D1/D0 can be reduced, where D1 is a length of a segmentpassing through the support area of the piezoelectric laminatedstructure on the straight line existing between the diaphragms 23 of theadjacent thin film piezoelectric resonators and D0 is a distance betweenthe diaphragm centers of the adjacent thin film piezoelectric resonators(see FIGS. 3A and 3B). This also applies to a relation between theelectrically connected adjacent thin film piezoelectric resonators 210and 240, and that between the electrically connected adjacent thin filmpiezoelectric resonators 220 and 240. This also applies to a relationbetween the electrically connected adjacent thin film piezoelectricresonators 210 and 230, and that between the electrically connectedadjacent thin film piezoelectric resonators 220 and 250. In these cases,the electric connection is performed via the lower electrode 15.

The thin film piezoelectric device of the present embodiment is a thinfilm piezoelectric filter constituted by a ladder type circuit in whichthe thin film piezoelectric resonators 210, 220 are connected in seriesto each other, and these resonators are branched/connected to the thinfilm piezoelectric resonators 230, 240, and 250.

As the substrate 12 of the thin film piezoelectric device of the presentinvention, a semiconductor single crystal such as a silicon (100) singlecrystal, or a polycrystal film such as diamond formed on the substratesurface of a silicon wafer or the like is usable. As the substrate 12,another semiconductor or insulating substrate may be used.

In the present invention, a substrate portion disposed under the portionconstituting the diaphragm constituting the vibration portion isanisotropically removed by a deep graving type reactive ion etching(deep RIE) process which is deep trench etching utilizing plasma tofabricate the via hole 22 in the substrate 12. For example, when thesubstrate is made of silicon, an SF₆ gas and a C₄F₈ gas are alternatelyintroduced into an etching equipment to repeat the etching and theformation of a side wall protective film. Accordingly, an etching speedratio of the side wall surface to the bottom surface is controlled, anda deep via hole having a prismatic or columnar side wall surface isvertically formed at the etching speed of several micrometers perminute. Therefore, planar shape and dimension of the diaphragm 23 aresubstantially equal to those of an opening 24 in the lower surface ofthe substrate, and the diaphragms 23 of the adjacent resonators can beremarkably brought close to each other. For example, when the diaphragm23 having a transverse dimension of about 150 μm×150 μm is formed whilefoaming the undersurface-side etching opening 24 having the equaldimension, the distance between the diaphragm centers of the adjacentresonators can be set to a value around 180 μm.

Accordingly, the FBAR resonators can be integrated with high density,and the insertion loss of the thin film piezoelectric device 200prepared by combining the FBAR resonators 210, 220, 230, 240, further250 can be remarkably reduced, because the electric resistance of themetal electrode is reduced in electrically connecting the adjacentresonators to each other using the metal electrodes (lower electrode 15and upper electrode 17) holding the piezoelectric film 16 therebetween.It is to be noted that the gap formed in the substrate 12 is not limitedto the gap by the via hole 22, and may have another configuration aslong as the vibration of the diaphragm 23 constituting the vibrationportion is allowed.

As the insulating layer 13, a dielectric film containing silicon oxide(SiO₂) or silicon nitride (Si₃N₄ or SiN_(x)) as a main component isusable. As to the material of this insulating layer 13, the maincomponent indicates a component whose content in the dielectric film is50% or more by equivalent ratio. The dielectric film may comprise asingle layer, or a plurality of layers in which layers (adhesive layers)for enhancing adhesion is included. Examples of the dielectric filmcomprising a plurality of layers include lamination of theabove-described silicon oxide (SiO₂) layer and the silicon nitride(Si₃N₄ or SiN_(x)) layer. The insulating layer 13 has a thickness of,for example, 0.2 to 1.0 μm. Examples of a method of forming theinsulating layer 13 include a method of thermally oxidizing the surfaceof the substrate 12 made of silicon, and a chemical vapor deposition(CVD) method. Furthermore, the dielectric film existing in the diaphragmportion may be completely removed.

As the lower electrode 15 and the upper electrode 17, a conductive filmof molybdenum (Mo), tungsten (W), platinum (Pt), gold (Au) or the likeis usable. Mo has a low thermal elastic loss which is about 1/56 of thatof Al, and is therefore preferable especially for constituting thevibration portion which vibrates at a high frequency. It is alsopossible to use an alloy containing Mo or W as the main component(preferably the content is 80 atomic % or more), in addition to the casewhere Mo alone or W alone is used. The electrode may be used in whichMo, W, Pt, or Au is laminated with the substrate layer (adhesive layer)for enhancing the adhesion of titanium (Ti), zirconium (Zr), chromium(Cr) or the like. For example, a Mo/Ti laminated film, a W/Ti laminatedfilm, a Mo/Zr laminated film, a Pt/Ti laminated film, an Au/Ti laminatedfilm, an Au/Cr laminated film or the like is usable. The thickness ofthe lower electrode 15 or the upper electrode 17 is, for example, 50 to250 nm. Examples of a method of forming the lower electrode 15 and theupper electrode 17 include a sputtering method or vacuum evaporationmethod. Furthermore, a photolithography technique is applied for forminga pattern into a desired shape if necessary.

The piezoelectric film 16 is constituted of a piezoelectric filmcontaining a piezoelectric material selected from an aluminum nitride(AlN), an aluminum nitride-gallium nitride based solid solution(Al_(1-x)Ga_(x)N (0<x<1)), zinc oxide (ZnO), lead titanate (PT(PbTiO₃)),lead zirconate titanate (PZT(Pb(Zr, Ti)O₃)) and the like as the maincomponent. The piezoelectric thin film made of aluminum nitride-galliumnitride based solid solution (Al_(1-x)Ga_(x)N) and zinc oxide (ZnO)indicates a c-axis orientation, and a rocking curve half value width(FWHM) of a (0002) surface measured by an X-ray diffraction method isnarrow. When the rocking curve half value width (FWHM) increases, andthe orientation drops, an electromechanical coupling coefficient K_(t) ²drops, there is a tendency that a pass bandwidth necessary for formingthe device cannot be taken, and resonance characteristic tends to bedeteriorated. The thickness of the piezoelectric film 16 is, forexample, 0.5 to 2.5 μm. Examples of a method of depositing thepiezoelectric film 16 include a reactive sputtering method, and furthera photolithography technique for forming the pattern into the desiredshape is applied if necessary.

FIG. 4A is a schematic plan view showing still another embodiment of thethin film piezoelectric device according to the present invention, andFIG. 4B is an explanatory diagram showing each distance betweendiaphragms. Also in these figures, members having functions similar tothose in FIGS. 1A to 3B described above are denoted with the samereference numerals. A thin film piezoelectric device 220, of FIGS. 4Aand 4B is prepared by combining an FBAR 210, an FBAR 220, an FBAR 230,an FBAR 240, and an FBAR 250.

In the present invention, in a straight line connected to centers (i.e.,centers 1 to 5 of the diaphragm) of the electrically connected adjacentthin film piezoelectric resonators, a ratio D1/D0 is 0.1 to 0.5, whereD1 is a length of a segment passing through the support area of thepiezoelectric laminated structure on the straight line existing betweenthe adjacent thin film piezoelectric resonators and D0 is a distancebetween the centers of the adjacent thin film piezoelectric resonators.A plurality of thin film piezoelectric resonators are arrangement insuch positions, and formed into a device. In the thin film piezoelectricdevice 200 of FIGS. 4A and 4B, as to the straight line connected to thecenters of the adjacent thin film piezoelectric resonators, assumingthat the lengths of the segments passing through the diaphragms of theadjacent thin film piezoelectric resonators are D2, D3, and the lengthof the segment passing through the support area existing between theadjacent thin film piezoelectric resonators is D1, as shown in FIG. 4B,the distance D0 between the centers of the adjacent thin filmpiezoelectric resonators is represented by:D0=D1+D2+D3.

FIG. 5A is a schematic plan view showing still another embodiment of thethin file piezoelectric device according to the present invention, andFIG. 5B is an explanatory diagram showing each distance betweendiaphragms. Also in these figures, members having functions similar tothose in FIGS. 1A to 4B described above are denoted with the samereference numerals. A thin film piezoelectric device 200 of FIGS. 5A and5B is prepared by combining an FBAR 210, an FBAR 220, an FBAR 230, andan FBAR 240.

In the thin film piezoelectric resonator of the present invention, theplanar shape of the diaphragm constituting the vibration portion isdevised and optimized. Accordingly, the thin film piezoelectric deviceis manufactured in which any extra spurious signal or noise does notenter a pass band and which has a low insertion loss and highcharacteristic and performance. Concrete examples of the preferableplanar shape of the diaphragm include: a shape (quadrangle) having twopairs of opposite sides in such a manner that at least one pair ofopposite sides are formed to be non-parallel; a polygonal shapeincluding a non-square irregular polygonal shape in at least a part ofthe shape; a non-square irregular polygonal shape including a curvedportion in at least a part of the shape and the like. The thin filmpiezoelectric device 200 of FIGS. 5A and 5B show an example of thequadrangle whose two pairs of opposite sides are both formed to benon-parallel. Also in the thin film piezoelectric device 200 of thesefigures, as to the straight line connected to the centers of theadjacent thin film piezoelectric resonators, assuming that the lengthsof the segments passing through the diaphragms of the adjacent thin filmpiezoelectric resonators are D2, D3, and the length of the segmentpassing through the support area existing between the adjacent thin filmpiezoelectric resonators is D1, as shown in FIG. 5B, the distance D0between the centers of the adjacent thin film piezoelectric resonatorsis represented by:D0=D1+D2+D3.

In the embodiment of the thin film piezoelectric device shown in FIGS.4A and 4B and FIGS. 5A and 5B, the FBAR 220 has a piezoelectriclaminated structure 14 prepared on the upper surface of the substrate.The piezoelectric laminated structure 14 comprises a lower electrode 15formed on the upper surface of the insulating layer, a piezoelectricfilm 16 formed on the upper surface of the insulating layer in such amanner as to coat the lower electrode 15, and an upper electrode 17formed on the upper surface of the piezoelectric film 16. The lowerelectrode 15 and the upper electrode 17 have main body portions 15 a, 17a formed in an area corresponding to the diaphragm 23, and terminalportions 15 b, 17 b for connection of the main body portions 15 a, 17 ato the other FBAR or an external circuit. The terminal portions 15 b, 17b extend to the outside of the area corresponding to the diaphragm. Thisalso applies to constitutions of the FBAR 210, FBAR 230, FBAR 240, andFBAR 250.

In the FBAR 210, FBAR 220, FBAR 230, and FBAR 240 shown in FIGS. 5A and5B, the diaphragm constituting the vibration portion is formed in such amanner that the planar shape is a quadrangle whose two pairs of oppositesides are both non-parallel, and symmetry of the diaphragm is lowered.Accordingly, any extra spurious signal or noise cannot enter the desiredpass band, and the performance of the thin film piezoelectric device foruse as a high-frequency circuit component is enhanced.

FIG. 9 is a schematic sectional plan view showing still anotherembodiment of the thin film piezoelectric device according to thepresent invention. Also in these figures, members having functionssimilar to those in FIGS. 1A to 5B described above are denoted with thesame reference numerals.

The present embodiment has SBARs 210′ and 220′ each comprising apiezoelectric laminated structure corresponding to two laminatedpiezoelectric laminated structures described in the above embodiments.That is, a lower electrode 15, a first piezoelectric film 16-1, innerelectrodes 17′, a second piezoelectric film 16-2, and upper electrodes18 are stacked in this order on an insulating layer 13. The innerelectrode 17′ has a function of an upper electrode with respect to thefirst piezoelectric film 16-1, and a function of a lower electrode withrespect to the second piezoelectric film 16-2. In the presentembodiment, in each SBAR, an input voltage is applied between the lowerelectrode 15 or the upper electrode 18 and the inner electrode 17′, avoltage between the upper electrode 18 or the lower electrode 15 and theinner electrode 17′ can be taken out as an output voltage, and this canbe used as a multipolar filter.

SBARs 210′, 220′ are electrically connected to each other via the lowerelectrode 15. The SBARs 210′, 220′ may be electrically connected to eachother via the upper electrode 18 or the inner electrode 17′.

Also in the present embodiment, a plurality of SBARs are arranged inpositions where a ratio D1/D0 of a length D1 of a segment passingthrough a support area of a piezoelectric laminated structure in which astraight line exists between adjacent SBARs to a distance D0 betweencenters of the adjacent SBARs is 0.1 to 0.5 in the straight lineconnected to the centers of diaphragms 23 of electrically connectedadjacent SBARs.

In each thin film piezoelectric resonator constituting theabove-described thin film piezoelectric device, a resonant frequency frand an antiresonant frequency fa in an impedance characteristic measuredusing a microwave prober, and an electromechanical coupling coefficientK_(t) ² have the following relations:K _(t) ² =φr/Tan(φr); and

φr=(π/2) (fr/fa), where φr indicates a change of a phase of a compleximpedance.

For the sake of simplicity, the electromechanical coupling coefficientK_(t) ² calculated from the following equation is usable:K _(t) ²=4.8(fa−fr)/(fa+fr).In the present description, a numeric value of the electromechanicalcoupling coefficient K_(t) ² calculated using this equation is adopted.

The present inventors have studied dependence of the characteristics andperformances of the thin film piezoelectric devices constituted as shownin FIGS. 1A to 1C, 2A to 2C, 3A and 3B, 4A and 4B, 5A and 5B, and 9 onstructures and arrangements of FBARs, SBARs constituting the thin filmpiezoelectric devices. As a result, it has been found that the distancebetween the diaphragm centers of the electrically connected adjacentthin film piezoelectric resonators is shortened, preferably the planarshape of the diaphragm is optimized, accordingly the insertion lossattributable to the conductor loss of the metal electrode can beremarkably reduced, a plurality of thin film piezoelectric resonatorshaving satisfactory resonance chartacteristics are integrated with highdensity, and a high-performance thin film piezoelectric device superiorin gain and band characteristic can be realized.

In the thin film piezoelectric device of the present invention, theelectromechanical coupling coefficient K_(t) ² obtained from themeasured values of the resonant frequency and the antiresonant frequencyin the vicinity of 2.0 GHz is preferably more than 4.0%. When theelectromechanical coupling coefficient is less than 4.0%, the bandwidthof the prepared thin film piezoelectric filter is reduced, and it tendsto be difficult to practically use the device as a filter for use in ahigh frequency band. The insertion loss is preferably 3.0 dB or less.When the insertion loss exceeds 3.0 dB, the filter characteristic isremarkably deteriorated, and it tends to be difficult to practically usethe device as the filter for use in the high frequency band.

EXAMPLES

The present invention will be described hereinafter in more detail inaccordance with examples and comparative examples.

Example 1

In the present example, a thin film piezoelectric filter shown in FIGS.2A to 2C was prepared as follows.

That is, the upper surface of a (100) Si substrate 12 having a thicknessof 250 μm was patterned and etched into a desired shape byphotolithography, so that a depression was disposed in periphery thereofin such a manner that a flat base having a nearly rectangular shape witha height of 3.0 μm and a planar dimension of about 140×160 μm was left.It is to be noted that the base was formed in a position correspondingto a diaphragm of an resonator to be formed. After forming SiO₂ layerseach having a thickness of 1.0 μm on opposite upper/lower surfaces of asubstrate by a thermal oxidation method, an SiO₂ layer having athickness of 3.5 μm was deposited on the upper surface of the substrateat 450° C. by a thermal CVD method using tetraethoxy silane(Si(O(C₂H₅)₄) in a raw material, and annealed at 1000° C. Next, the SiO₂layer on the upper surface of the substrate was polished by a chemicalmechanical polishing (CMP) process using a slurry containing finepolishing particles, an SiO₂ layer was completely removed from a regionexcept a portion whose depression was filled with the SiO₂ layer, and asurface state was obtained in which an Si substrate portion having theflat base shape was exposed to the outside. An RMS roughness of a heightof the polished surface was 10 nm. After the exposed portion of the Sisubstrate was etched/removed by a depth of about 0.3 μm using the SiO₂layer exposed to the surface as a bask, a Ti metal layer (adhesivelayer) and a Mo metal layer (main electrode layer) were deposited inthis order by a DC magnetron sputtering method, and a lower electrodefilm containing Mo having a material and a thickness described in Table1 as a main material was formed. The lower electrode film was patternedinto a desired shape by photolithography, and a Mo/Ti lower electrode 15was formed. A main body portion 15 a of the lower electrode 15 of eachFBAR was formed into a nearly rectangular shape whose each side waslarger than that of the diaphragm having a planar dimension of 140×160μm by about 15 μm. It was confirmed by X-ray diffraction measurementthat the Mo metal layer constituting the lower electrode 15 was a (110)oriented film, that is, a single orientation film. An AlN piezoelectricthin film having a thickness described in Table 2 was deposited on thesubstrate 12 on which the Mo/Ti lower electrode 15 was deposited onconditions described in Table 1 by a reactive RF magnetron sputteringmethod using metal Al having a purity of 5N as a target. The AlN filmwas patterned into a specific shape by wet etching using hot phosphoricacid, and an AlN piezoelectric film 16 was formed. Thereafter, as shownin FIGS. 2A to 2C, an upper electrode 17 was deposited using the DCmagnetron sputtering method and a lift-off process for patterning, inwhich the thickness was 0.180 μm for a series circuit and 0.209 μm for ashunt circuit, and a main body portion 17 a had a nearly rectangularshape whose each side was smaller than that of the diaphragm by about 5μm. The main body portion 17 a of the upper electrode 17 was disposed ina position corresponding to the lower electrode main body portion 15 a.

The SiO₂ layer on the lower surface of the substrate 12 on which apiezoelectric laminated structure 14 was formed as described above waspatterned into a predetermined shape in accordance with the SiO₂ mask onthe upper surface by the photolithography. Furthermore a micro machineworking photo resist (NANO SU-8-negative resist manufactured byMicroChem Corp.) was applied, and a resist mask having the same shape asthat of the lower-surface SiO₂ mask was formed by the photolithography.The substrate 12 on which the mask was formed was charged into a dryetching equipment having a deep graving type reactive ion etching (deepRIE) specification, and an SF₆ gas and a C₄F₈ gas were alternatelyintroduced into the equipment to repeat the etching and formation of aside wall protective film. An etching speed ratio of a side wall surfaceto a bottom surface was controlled, and the etching was continued at aspeed of several micrometers per minute. Accordingly, the etching wasperformed until the lower electrode 15 was exposed to a via hole 22, andthe deep prismatic via hole 22 whose side wall surface was verticallydisposed was prepared. As a result, it was possible to form thediaphragm 23 into a planar shape and a dimension substantially equal tothose of an opening 24 in the lower surface of the substrate. A value ofa ratio D1/D0 of a length D1 of a segment passing through a support areaof the piezoelectric laminated structure in which a straight linepassing through the centers of the diaphragms of two electricallyconnected adjacent thin film piezoelectric resonators existed betweenthe diaphragms of the adjacent thin film piezoelectric resonators to adistance D0 between the centers of the diaphragms of two adjacent thinfilm piezoelectric resonators was 0.18. The value of this ratio D1/D0indicates that of representative one set of electrically connectedadjacent thin film piezoelectric resonators, but the value of the ratioD1/D0 was in a range of 0.18 to 0.3 also with respect to another set ofelectrically connected adjacent thin film piezoelectric resonators.Tapered angle or club-shaped angles of side wall surfaces of all viaholes were in a range of 80 to 100° with respect to the upper surface ofthe substrate.

With respect to thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIGS. 2A to 2C, a lattice constant of an AlN thin film,and a rocking curve half value width (FWHM) of a (0002) diffraction peakwere measured by a diffractometer method. Evaluation results of thedegree of crystal orientation of the AlN thin film are shown in Table 1.

TABLE 1 Material and thickness of metal electrode Lower electrode Upperelectrode Adhesive Intermediate Adhesive Main layer layer Main ElectrodeThickness layer electrode Thickness material material layer material(nm) material layer material (nm)* Example 1 Ti — Mo 200 — Mo 180 208Example 2 Ti Pt Mo 230 Ti Mo 210 244 Example 3 Ti Au Mo 210 — Mo 190 225Example 4 V Au Mo 220 — Mo 200 (TZM alloy) (TZM alloy) 235 Example 5 TiAl Mo 225 — Mo 205 237 Example 6 Ti Au Mo 210 Ti Mo 190 228 Example 7 Ti— Mo 195 — Al 175 196 Example 8 Ti — Au 170 — Au 150 180 Example 9 Ti PtMo 235 Ti Mo 215 (TZM alloy) (TZM alloy) 250 Example 10 Zr Au Mo 205 ZrMo 185 219 Example 11 Ti — Pt 220 Ti Pt 200 240 Example 12 Ni Al W 225 —Al 205 222 Example 13 Nb Pt W—Mo 210 Nb W—Mo 190 alloy alloy 223 Example14 Hf — Pt 210 — Pt 190 211 Comparative Ni — Mo—Re 195 — Mo—Re 175example 1 alloy alloy 205 Comparative Ti — Mo 230 Ti Mo 210 example 2243 Comparative Ti — Au 160 — Au 140 example 3 158 Comparative Zr Au Mo210 — Mo 190 example 4 218 Preparation conditions and characteristics ofpiezoelectric thin film Thin film depositing Structure of thin-filmconditions Crystal piezoelectric device Nitrogen Substrate orientationInsulating layer concentration temperature rocking curve StructureThickness Material (vol %) (° C.) FWHM(deg) drawing Material (μm)**Example 1 AlN 30 350 2.4 FIG. 2 SiO₂ 0.00 Example 2 AlN 35 300 1.8 FIG.2 SiO₂ 0.00 Example 3 AlN 25 325 1.6 FIG. 1 SiO₂ 0.25 Example 4 (Al,Ga)N35 340 1.9 FIG. 1 SiO₂ 0.35 Example 5 AlN 50 315 1.7 FIG. 2 SiO₂ 0.00Example 6 AlN 50 305 1.4 FIG. 2 SiO₂ 0.00 Example 7 AlN 25 250 2.6 FIG.2 SiO₂ 0.00 Example 8 ZnO — 240 2.3 FIG. 3 SiO₂ 0.30 Example 9 AlN 45340 2.0 FIG. 1 SiNx 0.30 Example 10 AlN 35 280 2.2 FIG. 2 SiO₂ 0.00Example 11 PZT — 600 — FIG. 1 SiNx 0.43 Example 12 AlN 30 250 4.0 FIG. 1SiNx 0.40 Example 13 (Al,Ga)N 50 270 3.5 FIG. 1 SiO₂ 0.20 Example 14 ZnO— 270 3.6 FIG. 2 SiO₂ 0.00 Comparative AlN 45 345 3.2 FIG. 1 SiO₂ 0.38example 1 Comparative AlN 45 270 2.9 FIG. 8 SiO₂ 0.35 example 2Comparative ZnO — 260 3.0 FIG. 8 SiO₂ 0.40 example 3 Comparative AlN 40260 2.8 FIG. 2 SiO₂ 0.00 example 4 *Upper stage indicates thickness ofupper electrode in series circuit, lower stage indicates thickness ofupper electrode in shunt circuit. **Thickness of insulating layer indiaphragm portion is described.

Moreover, an impedance characteristic between the electrode terminals 15b, 17 b of the FBAR constituting the thin film piezoelectric filtercomprising a ladder type circuit was measured using a microwave proberand a network analyzer manufactured by Cascade Microtech Inc. Moreover,an electromechanical coupling coefficient K_(t) ² and an acousticquality factor Q were obtained from measured values of a resonantfrequency fr and antiresonant frequency fa.

The resonant frequency fr, antiresonant frequency fa, andelectromechanical coupling coefficient K_(t) ² in the resonancecharacteristic measured using the microwave prober have the followingrelation:K _(t) ² =φr/Tan(φr); and

φr=(π/2) (fr/fa), where φr indicates a change of a phase of a compleximpedance.

For the sake of simplicity, the electromechanical coupling coefficientK_(t) ² was calculated from the following equation:K _(t) ²=4.8(fa−fr)/(fa+fr).

A basic frequency of thickness vibration, the electromechanical couplingcoefficient K_(t) ², and the acoustic quality factor Q of the obtainedthin film piezoelectric filter are as shown in Table 2.

TABLE 2 Structure of thin-film Characteristics of piezoelectric devicethin-film Distance between Thickness of piezoelectric resonator*adjacent diaphragm piezoelectric Resonant Antiresonant Diaphragm D1 D2 +D3 D0 thin film frequency frequency shape (μm) (μm) (μm) D1/D0 (μm)(GHz) (GHz) Example 1 Rectangular 34 150 184 0.18 1.17 2.65 2.72 2.592.65 Example 2 Trapezoidal 35 150 185 0.19 1.32 2.45 2.51 2.39 2.45Example 3 Trapezoidal 35 150 185 0.19 1.50 1.91 1.96 1.87 1.91 Example 4Rectangular 33 135 168 0.20 1.30 1.85 1.89 1.81 1.85 Example 5Rectangular 50 160 210 0.24 1.40 2.36 2.42 2.30 2.36 Example 6Pentangular 53 170 223 0.24 1.57 2.12 2.18 2.06 2.12 Example 7Non-orthogonal 50 150 200 0.25 1.05 2.32 2.37 shape Including 2.26 2.32curves Example 8 Rectangular 44 180 224 0.20 0.98 1.35 1.39 1.31 1.35Example 9 Rectangular 38 160 198 0.19 1.20 2.20 2.25 2.15 2.20 Example10 Trapezoidal 35 150 185 0.19 1.40 2.25 2.31 2.20 2.25 Example 11Rectangular 50 150 200 0.25 0.58 1.72 1.78 1.67 1.72 Example 12Rectangular 55 175 230 0.24 0.99 2.06 2.09 2.03 2.06 Example 13Rectangular 40 165 205 0.20 1.30 2.16 2.20 2.12 2.16 Example 14Rectangular 35 140 175 0.20 1.02 1.89 1.93 1.86 1.89 ComparativeTrapezoidal 180 150 330 0.55 1.00 2.14 2.19 example 1 2.10 2.14Comparative Rectangular 450 160 610 0.74 1.05 2.09 2.13 example 2 2.052.09 Comparative Rectangular 450 150 600 0.75 0.41 1.70 1.74 example 31.67 1.70 Comparative Rectangular 20 190 210 0.095 1.50 2.29 2.34example 4 2.24 2.29 Characteristics of Performance of thin-filmthin-film piezoelectric device piezoelectric resonator* InhibitionElectromechanical region coupling Acoustic Pass Insertion altenuationcoefficient quality factor bandwidth Loss I.L. amount Kt²(%) Q-ValueType of device (MHz) (dB) (dB) Example 1 5.92 1012 Ladder-type filter66.3 1.8 45.6 Example 2 6.19 1256 Ladder-type filter 64.0 1.4 47.0Example 3 5.29 1757 Ladder-type filter 42.6 1.3 51.9 Example 4 5.13 1556Ladder-type filter 40.0 1.7 49.8 Example 5 6.27 1065 Ladder-type filter62.5 2.0 46.1 Example 6 6.50 1188 Ladder-type filter 58.2 1.7 47.3Example 7 5.88 941 Ladder-type filter 57.5 1.3 45.6 Example 8 6.98 650Ladder-type filter 39.8 1.9 45.3 Example 9 5.64 1351 Ladder-type filter52.3 2.3 46.0 Example 10 5.99 1100 Duplexer 56.9 1.4 46.3 (ladder-typefilter)** Example 11 8.13 189 Ladder-type filter 59.4 2.9 24.0 Example12 4.00 825 Ladder-type filter 34.6 1.6 39.7 Example 13 4.27 872Ladder-type filter 38.8 2.0 40.2 Example 14 4.33 500 Ladder-type filter34.5 2.5 35.4 Comparative 4.84 456 Ladder-type filter 43.7 5.0 26.2example 1 Comparative 4.96 539 Ladder-type filter 43.6 8.0 28.8 example2 Comparative 5.18 276 Ladder-type filter 37.1 6.0 25.1 example 3Comparative 5.20 — Broken during processing example 4 and cannot beformed into device. *Upper stage indicates frequency characteristic ofFBAR in series circuit, lower stage indicates frequency characteristicsof FBAR in shunt circuit. **As to duplexer, performance of Tx(transmission side) is described.

Furthermore, pass band characteristics of a signal of theabove-described thin film piezoelectric filter comprising the laddertype circuit was measured using the microwave prober manufactured byCascade Microtech Inc. and network analyzer, and performances (passbandwidth, insertion loss, attenuation amount at inhibition region) ofthe filter were evaluated. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the obtained thin filmpiezoelectric filter are as shown in Table 2.

Example 2

In the present example, a thin film piezoelectric filter having thestructure (the diaphragm 23 is trapezoidal) shown in FIG. 2 was preparedas follows.

That is, an procedure similar to that of Example 1 was repeated toprepare the thin film piezoelectric filter comprising the ladder typecircuit except that a Ti metal layer (adhesive layer), a Pt metal layer(intermediate layer), and a Mo metal layer (main electrode layer) weredeposited as a lower electrode in this order to form a Mo/Pt/Ti lowerelectrode 15 having a material and thickness described in Table 1, a Timetal layer (adhesive layer) and a Mo metal layer (main electrode layer)were deposited as an upper electrode in this order to form a Mo/Ti upperelectrode 17 having a material and thickness described in Table 1, andthe planar shape of a via hole fabricated by deep RIE was formed to betrapezoidal to thereby form a diaphragm 23 into a trapezoidal shape. Theabove described D1/D0 of the present example was 0.19. The value of thisratio D1/D0 indicates that of representative one set of electricallyconnected adjacent thin film piezoelectric resonators, but the value ofthe ratio D1/D0 was in a range of 0.18 to 0.3 also with respect toanother set of electrically connected adjacent thin film piezoelectricresonators. Tapered angle or club-shaped angles of side wall su faces ofall via holes were in a range of 80 to 100° with respect to the uppersurface of the substrate 5.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 2 (the diaphragm 23 was trapezoidal), a latticeconstant of an AlN thin film and a rocking curve half value width (FWHM)of a (0002) diffraction peak were measured by a diffractometer method inthe same manner as in Example 1. Evaluation results of the degree ofcrystal orientation of the AlN thin film are shown in Table 1.

Moreover, an electromechanical coupling coefficient K_(t) ² and anacoustic quality factor Q were obtained from measured values of aresonant frequency fr and antiresonant frequency fa of an FBARconstituting the above-described thin film piezoelectric filtercomprising the ladder type circuit using a microwave prober manufacturedby Cascade Microtech Inc. and a network analyzer in the same manner asin Example 1. A basic frequency of thickness vibration, theelectromechanical coupling coefficient K_(t) ², and the acoustic qualityfactor Q of the obtained thin film piezoelectric filter are as shownTable 2.

Furthermore, pass band characteristic of a signal of the above-describedthin film piezoelectric filter comprising the ladder type circuit wasmeasured, and performances (pass bandwidth, insertion loss, attenuationamount at inhibition region) of the filter were evaluated in the samemanner as in Example 1. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the obtained thin filmpiezoelectric filter are as shown in Table 2.

Example 3

In the present example, a thin film piezoelectric filter having thestructure (the diaphragm 23 was trapezoidal) shown in FIG. 1 wasprepared as follows.

That is, after forming SiO₂ layers each having a thickness of 1.2 μm onopposite upper/lower surfaces of a (100) Si substrate 12 having athickness of 250 μm by a thermal oxidation method, the only SiO₂ layeron the upper surface was etched to adjust the thickness of the SiO₂layer on the upper surface, and an insulating layer 13 made of SiO₂ andhaving a thickness value described in Table 1 was formed. A Ti metallayer (adhesive layer), an Au metal layer (intermediate layer), and a Mometal layer (main electrode layer) were deposited on the upper surfaceof the insulating layer 13 in this order by a DC magnetron sputteringmethod, and patterned into a desired shape by photolithography to form aMo/Au/Ti lower electrode 15. A main body portion 15 a of the lowerelectrode 15 was formed into a nearly rectangular shape. It wasconfirmed by X-ray diffraction measurement that the Mo metal layer was a(110) oriented film, that is, a singly oriented film. An AlNpiezoelectric thin film having a thickness described in Table 2 wasformed on the insulating layer 13 on which the Mo lower electrode 15 wasdeposited on conditions described in Table 1 by a reactive RF magnetronsputtering method using metal Al having a purity of 5N as a target. TheAlN film was patterned into a specific shape by wet etching using hotphosphoric acid, and an AlN piezoelectric film 16 was formed.Thereafter, as shown in FIG. 1, an upper electrode 17 was depositedusing the DC magnetron sputtering method and a lift-off process, inwhich the thickness was 0.190 μm for a series circuit and 0.225 μm for ashunt circuit, and a main body portion 17 a had a nearly rectangularshape whose planar area was around 23,000 μm². The main body portion 17a of the upper electrode 17 was disposed in a position corresponding tothe lower electrode main body portion 15 a.

The SiO₂ layer on the lower surface of the substrate 12 on which apiezoelectric laminated structure 14 was formed as described above waspatterned into a predetermined shape in accordance with the upperelectrode main body portion 17 a by the photolithography. Furthermore, amicro machine working photo resist (NANO SU-8 negative resistmanufactured by MicroChem Corp.) was applied, and a resist mask havingthe same shape as that of the lower-surface SiO₂ mask was formed by thephotolithography. The substrate 12 on which the mask was formed wascharged into a dry etching equipment having a deep graving type reactiveion etching (deep RIE) specification, and an SF₆ gas and a C₄F₈ gas werealternately introduced into the equipment to repeat the etching andformation of a side wall protective film. An etching speed ratio of aside wall surface to a bottom surface was controlled, and the etchingwas continued at a speed of several micrometers per minute. Accordingly,the etching was performed until the lower electrode main body portion 15a was exposed to a via hole 22, and the deep prismatic via hole 22 whoseside wall surface was vertically disposed was prepared. As a result, itwas possible to form the diaphragm 23 into a planar shape and adimension substantially equal to those of an opening 24 in the substrateback surface. The above-described D1/D0 of the present example was 0.19.The value of this ratio D1/D0 indicates that of representative one setof electrically connected adjacent thin film piezoelectric resonators,but the value of the ratio D1/D0 was in a range of 0.18 to 0.3 also withrespect to another set of electrically connected adjacent thin filmpiezoelectric resonators. Tapered angle or club-shaped angles of sidewall surfaces of all via holes were in a range of 80 to 100° withrespect to the upper surface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 1, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 1. Theevaluation results are shown in Table 1.

Moreover, an electromechanical coupling coefficient K_(t) ² and anacoustic quality factor Q were obtained from measured values of aresonant frequency fr and antiresonant frequency fa of an FBARconstituting the above-described thin film piezoelectric filtercomprising the ladder type circuit using a microwave prober and anetwork analyzer manufactured by cascade Microtech Inc. in the samemanner as in Example 1. A basic thickness vibration, theelectromechanical coupling coefficient K_(t) ², and the acoustic qualityfactor Q of the obtained thin film piezoelectric filter are as shown inTable 2.

Furthermore, pass band characteristic of a signal of the above-describedthin film piezoelectric filter comprising the ladder type circuit wasmeasured, and performances (pass bandwidth, insertion loss, attenuationamount at inhibition region) of the filter were evaluated in the samemanner as in Example 1. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the obtained thin filmpiezoelectric filter are as shown in Table 2.

Example 4

In the present example, a thin film piezoelectric filter having thestructure shown in FIG. 1 was prepared as follows.

That is, an procedure similar to that of Example 3 was repeated toprepare the thin film piezoelectric filter comprising the ladder typecircuit except that a V metal layer (adhesive layer), an Au metal layer(intermediate layer), and a TZM alloy layer (main electrode layer) wereformed as a lower electrode in this order to form a Mo (TZM alloy)/Au/Vlower electrode 15 having a material and thickness described in Table 1,an aluminum nitride-gallium nitride based solid solution(Al_(1-x)Ga_(x)N) having a thickness described in Table 2 was formed onan insulating layer 13 on which the Mo (TZM alloy)/Au/V lower electrode15 was formed by a reactive RF magnetron sputtering method on conditionsdescribed in Table 1, a Mo (TZM alloy) upper electrode 17 having amaterial and a thickness described in Table 1 was formed as an upperelectrode, and the planar shape of a via hole fabricated by deep RIE wasformed to be rectangular to thereby form a diaphragm 23 into arectangular shape. The above-described D1/D0 of the present example was0.20. The value of this ratio D1/D0 indicates that of representative oneset of electrically connected adjacent thin film piezoelectricresonators, but the value of the ratio D1/D0 was in a range of 0.18 to0.3 also with respect to another set of electrically connected adjacentthin film piezoelectric resonators. Tapered angle or club-shaped anglesof side wall surfaces of all via holes were in a range of 80 to 100°with respect to the upper surface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 1, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 3. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic ofthe signal of the thin film piezoelectric filter comprising the laddertype circuit were measured using a microwave prober and a networkanalyzer manufactured by Cascade Microtech Inc. in the same manner as inExample 3. An electromechanical coupling coefficient K_(t) ² and anacoustic quality factor Q were obtained from measured values of aresonant frequency fr and antiresonant frequency fa, and performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. Furthermore, the pass bandwidth, insertion lossI. L., and attenuation amount at inhibition region of the filter are asshown in Table 2.

Examples 5 to 7

In the present examples, a thin film piezoelectric filter having thestructure (the diaphragm 23 had a shape described in Table 1) shown inFIG. 2 was prepared as follows.

That is, an procedure similar to that of Example 1 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that a Ti adhesive layer, an intermediate layer, and a Mometal layer (main electrode layer) described in Table 1 were formed as alower electrode in this order to form a Mo/Al/Ti, Mo/Au/Ti, or Mo/Tilower electrode 15 having a material and thickness described in Table 1,an upper electrode 17 having a material and thickness described in Table1 and made of Mo, Mo/Ti, or Al was formed, and the shape of a diaphragm23 was formed into a shape described in Table 1 based on the planarshape of a via hole fabricated by deep RIE. The above-described D1/D0 ofthe present examples was 0.24 to 0.25 as shown in Table 2. The value ofthis ratio D1/D0 indicates that of representative one set ofelectrically connected adjacent thin film piezoelectric resonators, butthe value of the ratio D1/D0 was in a range of 0.18 to 0.3 also withrespect to another set of electrically connected adjacent thin filmpiezoelectric resonators. Tapered angle or club-shaped angles of sidewall surfaces of all via holes were in a range of 80 to 100° withrespect to the upper surface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 2 (the diaphragm 23 had a shape described in Table1), the degree of crystal orientation of the AlN thin, film wasevaluated in the same manner as in Example 1. The evaluation results areshown in Table 1.

Moreover, an impedance characteristic and pass band characteristic ofthe signal of the above-described thin film piezoelectric filtercomprising the ladder type circuit were measured using a microwaveprober and a network analyzer manufactured by Cascade Microtech Inc. inthe same manner as in Example 3, and an electromechanical couplingcoefficient K_(t) ² and an acoustic quality factor Q were obtained frommeasured values of a resonant frequency fr and antiresonant frequencyfa. Moreover, performances (pass bandwidth, insertion loss, attenuationamount at inhibition region) of the filter were evaluated. A basicfrequency of thickness vibration, the electromechanical couplingcoefficient K_(t) ², and the acoustic quality factor Q of the obtainedthin film piezoelectric filter are as shown in Table 2. The passbandwidth, insertion loss I. L., and attenuation amount at inhibitionregion of the obtained thin film piezoelectric filter are as shown inTable 2.

FIGS. 6A and 6B show an impedance frequency characteristic and a filterpass band characteristic of the thin film piezoelectric filter inExample 6. In the thin film piezoelectric filter of the present example,a fine peak between a resonant frequency peak 31 and an antiresonantfrequency peak 32 is remarkably little, and the pass band characteristicis remarkably satisfactory as shown in FIG. 6A. This satisfactory passband characteristic depends on a diaphragm shape which is an asymmetricpentagonal shape.

Example 8

In the present example, a thin film piezoelectric filter having thestructure shown in FIG. 3 was prepared as follows.

The is, an procedure similar to that of Example 3 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that a Ti metal layer (adhesive layer) and an Au metallayers (main electrode layer) were deposited as a lower electrode inthis order to form an Au/Ti lower electrode 15 having a material andthickness described in Table 1, a ZnO piezoelectric thin film having athickness described in Table 2 was formed on an insulating layer 13 onwhich the Au/Ti lower electrode 15 was deposited by an RF magnetronsputtering method on conditions described in Table 1 using ZnO as atarget, an Au upper electrode 17 constituted of two electrode portions17A, 17B having a thickness described in Table 1 was formed as an upperelectrode, and a diaphragm 23 was formed into a rectangular shape basedon the planar shape of a via hole fabricated by deep RIE. Theabove-described D1/D0 of the present example was 0.20. The value of thisratio D1/D0 indicates that of representative one set of electricallyconnected adjacent thin film piezoelectric resonators, but the value ofthe ratio D1/D0 was in a range of 0.18 to 0.3 also with respect toanother set of electrically connected adjacent thin film piezoelectricresonators. Tapered angle or club-shaped angles of side wall surfaces ofall via holes were in a range of 80 to 100° with respect to the uppersurface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 3, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 3. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic ofthe signal of the thin film piezoelectric filter comprising the laddertype circuit were measured using a microwave in the same manner as inExample 3. An electromechanical coupling coefficient K_(t) ² and anacoustic quality factor Q were obtained from measured values of aresonant frequency fr and antiresonant frequency fa, and performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. Furthermore, the pass bandwidth, insertion lossI. L., and attenuation amount at inhibition region of the filter are asshown in Table 2.

Example 9

In the present example, a thin film piezoelectric filter having astructure similar to that shown in FIG. 1 was prepared as follows.

That is, an procedure similar to that of Example 3 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that an SiN_(x) layer was deposited at 800° C. by alow-pressure CVD method using mono silane (SiH₄) and ammonia (NH₃) asraw materials instead of an SiO₂ layer formed by a thermal oxidationmethod, a main electrode layer of a lower electrode was changed to a TZMalloy layer from Mo, an intermediate layer of the lower electrode waschanged to Pt from Au and a Mo (TZM alloy)/Pt/Ti lower electrode 15having a material and thickness described in Table 1 was deposited, amain electrode layer of an upper electrode was changed to a TZM alloylayer from Mo, a Ti adhesive layer was used and a Mo (TZM alloy)/Tiupper electrode 17 having a material and thickness described in Table 1was deposited, a diaphragm 23 was formed into a rectangular shape basedon the planar shape of a via hole fabricated by deep RIE, andarrangement of FBARs each constituting the thin film piezoelectricfilter was changed to a lattice type circuit from a ladder type circuit.The above-described D1/D0 of the present example was 0.19. The value ofthis ratio D1/D0 indicates that of representative one set ofelectrically connected adjacent thin film piezoelectric resonators, butthe value of the ratio D1/D0 was in a range of 0.18 to 0.3 also withrespect to another set of electrically connected adjacent thin filmpiezoelectric resonators. Tapered angle or club-shaped angles of sidewall surfaces of all via holes were in a range of 80 to 100° withrespect to the upper surface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the lattice type circuit; thedegree of crystal orientation of the AlN thin film was evaluated in thesame manner as in Example 3. The evaluation results are shown in Table1.

Moreover, an impedance characteristic between electrode terminals 15 b,17 b of the FBAR constituting the thin film piezoelectric filtercomprising the lattice type circuit was measured using a microwaveprober and a network analyzer manufactured by Cascade Microtech Inc. Anelectromechanical coupling coefficient K_(t) ² and an acoustic qualityfactor Q were obtained from measured values of a resonant frequency frand antiresonant frequency fa. A basic frequency of thickness vibration,the electromechanical coupling coefficient K_(t) ², and the acousticquality factor Q of the obtained thin film piezoelectric filter are asshown in Table 2.

Furthermore, pass band characteristic of a signal of the thin filmpiezoelectric filter comprising the lattice type circuit was measuredusing a microwave prober and a network analyzer manufactured by CascadeMicrotech Inc., and performances (pass bandwidth, insertion loss,attenuation amount at inhibition region) of the filter were evaluated.The pass bandwidth, insertion loss I. L., and attenuation amount atinhibition region of the obtained thin film piezoelectric filter are asshown in Table 2.

Example 10

In the present example, a duplexer in which a thin fit piezoelectricfilter for transmission and a thin film piezoelectric filter forreception each having a structure (the diaphragm 23 was trapezoidal)shown in FIG. 2 are combined with a 90 degree phase matching unit wasprepared as follows.

That is, an procedure similar to that of Example 1 was repeated toprepare the thin film piezoelectric filters for transmission andreception constituted of ladder type circuits except that an adhesivelayer, an intermediate layer, and a main electrode layer described inTable 1 were deposited as a lower electrode in this order to form aMo/Au/Zr lower electrode 15 having a material and thickness described inTable 1, a Mo/Zr upper electrode 17 having a material and thicknessdescribed in Table 1 was deposited as an upper electrode, and the shapeof a diaphragm 23 was formed into a trapezoidal shape based on theplanar shape of a via hole fabricated by deep RIE. Next, these thin filmpiezoelectric filters were connected to each other via the 90 degreephase matching unit, and the duplexer shown in FIG. 10 was prepared.

In FIG. 10, a duplexer 300 includes a transmission thin filmpiezoelectric filter 310, a reception thin film piezoelectric filter330, and a 90 degree phase matching unit 350. One end of thetransmission thin film piezoelectric filter 310 is connected to atransmission port 302, and one end of the reception thin filmpiezoelectric filter 330 is connected to a reception port 304. The otherends of the transmission thin film piezoelectric filter 310 and thereception thin film piezoelectric filter 330 are connected to an antennaport 306 which is a port both for transmission/reception via the 90degree phase matching unit 350. That is, the 90 degree phase matchingunit 350 is connected to the antenna port 306, the transmission thinfilm piezoelectric filter 310, and the reception thin film piezoelectricfilter 330, respectively. The transmission port 302 is connected to atransmission circuit, the reception port 304 is connected to a receptioncircuit, and the antenna port 306 is connected to an antenna ANT. Thetransmission thin film piezoelectric filter 310 and the reception thinfilm piezoelectric filter 330 have chip-like configurations, and aremounted on a substrate on which the 90 degree phase matching unit 350and a desired wire-bonding are formed.

The above-described D1/D0 of the present example was 0.19. The value ofthis ratio D1/D0 indicates that of representative one set ofelectrically connected adjacent thin film piezoelectric resonators, butthe value of the ratio D1/D0 was in a range of 0.18 to 0.3 also withrespect to another set of electrically connected adjacent thin filmpiezoelectric resonators. Tapered angle or club-shaped angles of sidewall surfaces of all via holes were in a range of 80 to 100° withrespect to the upper surface of the substrate.

With respect to the thin film piezoelectric filter constituting theduplexer manufactured by the above-described steps and constituted ofthe ladder type circuit having the structure (the diaphragm 23, wastrapezoidal) of FIG. 2, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 1. Theevaluation results are shown in Table 1.

Moreover, a resonant frequency fr, an antiresonant frequency fa, anelectromechanical coupling coefficient K_(t) ², and an acoustic qualityfactor Q of the thin film piezoelectric filter constituting the duplexerand constituted of the above-described ladder type circuit were obtainedusing a microwave prober and a network analyzer manufactured by CascadeMicrotech Inc. in the same manner as in Example 1. A basic frequency ofthickness vibration, the electromechanical coupling coefficient K_(t) ²,and the acoustic quality factor Q of the obtained thin filmpiezoelectric filter are as shown in Table 2.

Furthermore, pass band characteristic of a signal of the thin filmpiezoelectric filter constituting the duplexer and constituted of theabove-described ladder type circuit was measured in the same manner asin Example 1, and performances (pass bandwidth insertion loss,attenuation amount at inhibition region) of the filter were evaluated.The pass bandwidth, insertion loss I. L., and attenuation amount atinhibition region of the obtained thin film piezoelectric filter are asshown in Table 2.

Examples 11, 12

In the present examples, a thin film piezoelectric filter having astructure shown in FIG. 1 was prepared as follows.

That is, an procedure similar to that of Example 9 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that an adhesive layer, an intermediate layer, and a mainelectrode layer described in Table 1 were deposited as a lower electrodein this order to form a lower electrode 15 having a material andthickness described in Table 1 and made of Pt/Ti or W/Al/Ni, a PZT(Pb(Zr, Ti)O₃) piezoelectric thin film or an AlN piezoelectric thin filmhaving a thickness described in Table 2 was formed on an insulatinglayer 13 on which the Pt/Ti or W/Al/Ni lower electrode 15 was depositedby an RF magnetron sputtering method or a reactive RF magnetronsputtering method on conditions described in Table 1, and an upperelectrode 17 having a thickness described in Table 1 and made of Pt/Tior Al was formed as an upper electrode. The above-described D1/D0 of thepresent example is as shown in Table 2. The value of this ratio D1/D0indicates that of representative one set of electrically connectedadjacent thin film piezoelectric resonators, but the value of the ratioD1/D0 was in a range of 0.18 to 0.3 also with respect to another set ofelectrically connected adjacent thin film piezoelectric resonators.Tapered angle or club-shaped angles of side wall surfaces of all viaholes were in a range of 80 to 100° with respect to the upper surface ofthe substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 1, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 3. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic of asignal of the thin film piezoelectric filter comprising the ladder typecircuit were measured using a microwave prober and a network analyzermanufactured by Cascade Microtech Inc. in the same manner as in Example3, and an electromechanical coupling coefficient K_(t) ² and an acousticquality factor Q were obtained from measured values of a resonantfrequency fr and an antiresonant frequency fa. Moreover, performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the filter are as shown inTable 2.

Example 13

In the present example, a thin film piezoelectric filter having astructure shown in FIG. 1 was prepared as follows.

That is, an procedure similar to that of Example 3 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that an Nb metal layer (adhesive layer), a Pt metallayer(intermediate layer), and a W—Mo alloy layer (main electrode layer)were deposited as a lower electrode in this order to form a W—Moalloy/Pt/Nb lower electrode 15 having a material and thickness describedin Table 1, and an aluminum nitride-gallium nitride based solid solution(Al_(1-x)Ga_(x)N) having a thickness described in Table 2 was formed onan insulating layer 13 on which the W—Mo alloy/Pt/Nb lower electrode 15was deposited by a reactive RF magnetron sputtering method on conditionsdescribed in Table 1, a W—Mo alloy/Nb upper electrode 17 having amaterial and thickness described in Table 1 was formed as an upperelectrode, and a diaphragm 23 was formed into a rectangular shape basedon the planar shape of a via hole fabricated by deep RIE. Theabove-described D1/D0 of the present example was 0.20. The value of thisratio D1/D0 indicates that of representative one set of electricallyconnected adjacent thin film piezoelectric resonators, but the value ofthe ratio D1/D0 was in a range of 0.18 to 0.3 also with respect toanother set of electrically connected adjacent thin film piezoelectricresonators. Tapered angle or club-shaped angles of side wall surfaces ofall via holes were in a range of 80 to 100° with respect to the uppersurface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 1, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 3. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic of asignal of the thin film piezoelectric filter comprising the ladder typecircuit were measured using a microwave prober and a network analyzermanufactured by Cascade Microtech Inc. in the same manner as in Example3, and an electromechanical coupling coefficient K_(t) ² and an acousticquality factor Q were obtained from measured values of a resonantfrequency fr and an antiresonant frequency fa. Moreover, performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the filter are as shown inTable 2.

FIGS. 7A and 7B show the impedance frequency characteristic and filterpass band characteristic of the thin film piezoelectric device inExample 13. As seen when comparing FIGS. 6A and 6 (Example 6) with FIGS.7A and 7B (present example), in FIG. 7A of the present example, manyfine peaks exist between a resonant frequency peak 31 and anantiresonant frequency peak 32. On the other hand, in FIG. 6A of Example6, there is remarkably few fine peaks between the resonant frequencypeak 31 and the antiresonant frequency peak 32. Therefore, as seen whencomparing the filter pass band characteristic of FIG. 6B with that ofFIG. 7B, the pass band characteristic of the thin film piezoelectricfilter of Example 6 is more satisfactory. A difference between the passband characteristics mainly depends on the diaphragm shape, and it isindicate that an asymmetric pentangular shape is more preferable than arectangular shape.

Example 14

In the present example, a thin film piezoelectric filter having astructure shown in FIG. 2 was prepared as follows.

That is, an procedure similar to that of Example 1 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that an adhesive layer and a main electrode layerdescribed in Table 1 were deposited as a lower electrode in this orderto form a Pt/Hf lower electrode 15 having a material and thicknessdescribed in Table 1, a Pt upper electrode 17 having a thicknessdescribed in Table 1 was formed as an upper electrode, and a ZnOpiezoelectric thin film having a thickness described in Table 2 wasdeposited as a piezoelectric film on conditions described in Table 1 byan RF magnetron sputtering method using ZnO as a target. Theabove-described D1/D0 of the present example was 0.20. The value of thisratio D1/D0 indicates that of representative one set of electricallyconnected adjacent thin film piezoelectric resonators, but the value ofthe ratio D1/D0 was in a range of 0.18 to 0.3 also with respect toanother set of electrically connected adjacent thin film piezoelectricresonators. Tapered angle or club-shaped angles of side wall surfaces ofall via holes were in a range of 80 to 100° with respect to the uppersurface of the substrate.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIG. 2, the degree of crystal orientation of the AlNthin film was evaluated in the same manner as in Example 1. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic of asignal of the thin film piezoelectric filter comprising the ladder typecircuit were measured using a microwave prober and a network analyzermanufactured by Cascade Microtech Inc. in the same manner as in Example1, and an electromechanical coupling coefficient K_(t) ² and an acousticquality factor Q were obtained from measured values of a resonantfrequency fr and an antiresonant frequency fa. Moreover, performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the filter are as shown inTable 2

Comparative Example 1

In the present comparative example, a thin film piezoelectric filterhaving a structure (a diaphragm 23 was trapezoidal) shown in FIGS. 1A to1C was prepared as follows.

That is, an procedure similar to that of Example 3 was repeated toprepare the thin film piezoelectric filter comprising a ladder typecircuit except that an Ni metal layer (adhesive layer) and a Mo—Re alloylayer (main electrode layer) were deposited as a lower electrode in thisorder to form a Mo—Re alloy/Ni lower electrode 15 having a material andthickness described in Table 1, an AlN thin film having a thicknessdescribed in Table 2 was formed on an insulating layer 13 on which theMo—Re alloy/Ni lower electrode 15 was deposited by a reactive RFmagnetron sputtering method on conditions described in Table 1, and aMo—Re upper electrode 17 having a material and thickness described inTable 1 was formed as an upper electrode. The above-described D1/D0 ofthe present comparative example was 0.55. The value of this ratio D1/D0indicates that of representative one set of electrically connectedadjacent thin film piezoelectric resonators, but the value of the ratioD1/D0 was in a range of 0.5 to 0.6 also with respect to another set ofelectrically connected adjacent thin film piezoelectric resonators.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure (the diaphragm 23 was trapezoidal) of FIG. 1, the degreeof crystal orientation of the AlN thin film was evaluated in the samemanner as in Example 3. The evaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic of asignal of the thin film piezoelectric filter comprising the ladder typecircuit were measured using a microwave prober and a network analyzermanufactured by Cascade Microtech Inc. in the same manner as in Example3, and an electromechanical coupling coefficient K_(t) ² and an acousticquality factor Q were obtained from measured values of a resonantfrequency fr and an antiresonant frequency fa. Moreover, performances(pass bandwidth, insertion loss, attenuation amount at inhibitionregion) of the filter were evaluated. A basic frequency of thicknessvibration, the electromechanical coupling coefficient K_(t) ², and theacoustic quality factor Q of the obtained thin film piezoelectric filterare as shown in Table 2. The pass bandwidth, insertion loss I. L., andattenuation amount at inhibition region of the filter are as shown inTable 2.

Comparative Examples 2, 3

In the present comparative examples, a thin film piezoelectric filterhaving a structure shown in FIGS. 8A and 8B was prepared as follows.

That is, after forming SiO₂ layers each having a thickness of 1.0 μm onopposite upper/lower surfaces of a (100) Si substrate 12 having athickness of 300 μM at 1100° C. by a thermal oxidation method, the onlySiO₂ layer on the upper surface was etched to adjust the thickness ofthe SiO₂ layer on the upper surface, and an insulating layer 13 made ofSiO₂ and having a thickness value described in Table 1 was formed. Anadhesive layer and a main electrode layer described in Table 1 weredeposited on the upper surface of the insulating layer 13 in this orderby a DC magnetron sputtering method, and the layers were pattered into adesired shape by photolithography to form a Mo/Ti or Au/Ti lowerelectrode 15. A main body portion 15 a of the lower electrode 15 wasformed into a nearly rectangular shape whose each side was larger thanthat of the diaphragm 23 by about 40 μm. It was confirmed by X-raydiffraction measurement that the Mo metal layer was a (110) orientedfilm, that is, a singly oriented film. An AlN piezoelectric thin film ora ZnO piezoelectric thin film having a thickness described in Table 2was formed on the insulating layer 13 on which the Mo lower electrode 15was deposited on conditions described in Table 1 by a reactive RFmagnetron sputtering method using metal Al as a target or by an RFmagnetron sputtering method using ZnO as a target. The AlN film waspatterned into a specific shape by wet etching using hot phosphoricacid, or the ZnO film was patterned into a predetermined shape by wetetching using a phosphoric acid-hydrochloric acid mixed aqueoussolution, and an AlN or ZnO piezoelectric film 16 was formed.

Thereafter, an upper electrode 17 having a main body portion 17 a havinga shape close to a rectangular shape whose each side was smaller thanthat of the diaphragm 23 by about 5 μm and made of Mo/Ti or Au wasformed in a material and thickness described in Table 1 using the DCmagnetron sputtering method and a lift-off process. The main bodyportion 17 a of the upper electrode 17 was disposed in a positioncorresponding to the lower electrode main body portion 15 a.

The 1.0 μm thick SiO₂ layer formed on the lower surface of the Sisubstrate 12 on which a piezoelectric laminated structure 14 constitutedof the lower electrode 15, upper electrode 17, and piezoelectric film 16was formed as described above was patterned by the photolithography, anda mask for wet etching was prepared. The piezoelectric laminatedstructure 14 formed on the upper surface of the Si substrate 12 wascoated with a protective wax, and a portion of the Si substrate 12corresponding to the diaphragm 23 was etched/removed by heated KOH usingthe SiO₂ mask formed on the lower surface to prepare via holes 22constituting gaps. As a result, the planar dimension of the diaphragmwas around 150 μm×150 μm or 160 μm×160 μm, and the via hole was obtainedin which the planar dimension of the opening in the substrate backsurface was 575 μm×575 μm or 585 μm×585 μm. The above-described D1/D0 ofthe present comparative examples is as shown in Table 2. The value ofthis ratio D1/D0 indicates that of representative one set ofelectrically connected adjacent thin film piezoelectric resonators, butthe value of the ratio D1/D0 was in a range of 0.7 to 0.8 also withrespect to another set of electrically connected adjacent thin filmpiezoelectric resonators.

With respect to the thin film piezoelectric filter manufactured by theabove-described steps and constituted of the ladder type circuit havingthe structure of FIGS. 8A and 8B, the degree of crystal orientation ofthe AlN thin film was evaluated in the same manner as in Example 3. Theevaluation results are shown in Table 1.

Moreover, an impedance characteristic and pass band characteristic of asignal of the above-described thin film piezoelectric filter comprisingthe ladder type circuit were measured using a microwave prober and anetwork analyzer manufactured by Cascade Microtech Inc. in the samemanner as in Example 3, and an electromechanical coupling coefficientK_(t) ² and an acoustic quality factor Q were obtained from measuredvalues of a resonant frequency fr and antiresonant frequency fa.Moreover, performances (pass bandwidth, insertion loss, attenuationamount at inhibition region) of the filter were evaluated. A basicfrequency of thickness vibration, the electromechanical couplingcoefficient K_(t) ², and the acoustic quality factor Q of the obtainedthin film piezoelectric filter are as shown in Table 2. The passbandwidth, insertion loss I. L., and attenuation amount at inhibitionregion of the filter are as shown in Table 2.

Comparative Example 4

In the present comparative example, preparation of a thin filmpiezoelectric filter having a structure shown in FIG. 2 was tried insuch a manner that the above-described D1/D0 was 0.095.

That is, an procedure similar to that of Example 1 was repeated to tryto prepare the thin film piezoelectric filter comprising a ladder typecircuit except that a Zr metal layer (adhesive layer), an Au metal layer(intermediate layer), and a Mo metal layer (main electrode layer) weredeposited as a lower electrode in this order to form a Mo/Au/Zr lowerelectrode 15 having a material and thickness described in Table 1, and aMo upper electrode 17 having a thickness described in Table 1 was formedas an upper electrode. However, a dimension D1 corresponding to a widthof a support area existing between adjacent diaphragms was small,therefore a substrate was broken during working such as dicing or chipforming, and it was not possible to form the thin film piezoelectricfilter into a device. Therefore, it was not possible to evaluatecharacteristics of an FBAR or a filter.

With respect to a sample from which the preparation of the thin filmpiezoelectric filter was tried by the above-described steps, the degreeof crystal orientation of the AlN thin film was evaluated in the samemanner as in Example 1. The evaluation results are shown in Table 1.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, a substrateportion present under a portion constituting a vibration portion isanisotropically removed from the lower surface of a substrate by a deepgraving type reactive ion etching (deep RIE) process which is deeptrench etching utilizing plasma, and accordingly a via hole whichenables a small difference between a dimension of a diaphragm and thatof a lower surface opening of the substrate can be prepared.Accordingly, a distance between diaphragm centers of the adjacent thinfilm piezoelectric resonators of a thin film piezoelectric device, whichare electrically connected to each other by a metal electrode, isshortened, and an insertion loss attributable to a conductor loss of ametal electrode can be remarkably reduced.

According to a thin film piezoelectric device of the present invention,the distance between the diaphragm centers of the electrically connectedadjacent thin film piezoelectric resonators is short, and a plurality ofthin film piezoelectric resonators disposed in vicinity positions arecombined and integrated. Accordingly, the insertion loss attributable tothe conductor loss of the metal electrode can be remarkably reduced, anda thin film piezoelectric device ran be realized having a low insertionloss and having superior electromechanical coupling coefficient oracoustic quality factor (Q). A planar shape of the diaphragmconstituting the vibration portion of the thin film piezoelectricresonator is devised and optimized. Accordingly, there can be obtained athin film piezoelectric device having a low insertion loss and superiorpass band characteristics, in which any extra spurious signal or noisedoes not enter a pass band. When the thin film piezoelectric device ofthe present invention is used, the insertion loss is small, and the passband characteristics are superior. Therefore, a performance of a thinfilm piezoelectric oscillator (VCO), a filter, or a duplexer isenhanced, and the present invention can be utilized as various devicesfor mobile communication apparatuses.

1. A thin film piezoelectric device including a substrate having aplurality of vibration spaces and a piezoelectic laminated structureformed on the substrate, a plurality of thin film piezoelectricresonators being formed facing the vibration spaces, wherein thepiezoelectric laminated structure has at least a piezoelectric film anda metal electrode formed on at least a part of each of opposite surfacesof the piezoelectric film, the piezoelectric laminated structurecomprises diaphragms positioned facing the vibration spaces, and asupport area other than the diaphragms, at least one set of two adjacentthin film piezoelectric resonators are electrically connected to eachother through the metal electrode, the thin film piezoelectric devicecomprising at least one set of two adjacent thin film piezoelectricresonators in which D0 is a distance between the centers of thediaphragms of the two electrically connected adjacent thin filmpiezoelectric resonators and D1 is a length of a segment of a supportarea on a straight line passing through centers of the diaphragms of twoelectrically connected adjacent thin film piezoelectric resonators, anda ratio D1/D0 is 0.1 to 0.5.
 2. The thin film piezoelectric deviceaccording to claim 1, wherein the ratio D1/D0 is in a range of 0.1 to0.5 with respect to all the sets of two electrically connected adjacentthin film piezoelectric resonators.
 3. The thin film piezoelectricdevice according to claim 1, wherein each of the vibration spaces isformed by a via hole extending from the surface of the substrate onwhich the piezoelectric laminated structure is formed to the oppositesurface, and a side wall surface of the via hole forms a slant angle ina range of 80 to 100.degree. with respect to the surface of thesubstrate on which the piezoelectric laminated structure is formed. 4.The thin film piezoelectric device according to claim 1, wherein thepiezoelectric laminated structure comprises a lower electrodeconstituting the metal electrode, the piezoelectric film, and an upperelectrode constituting the metal electrode stacked in order from thesubstrate side in at least one thin film piezoelectric resonator.
 5. Thethin film piezoelectric device according to claim 4, wherein the upperelectrode of the at least one thin film piezoelectric resonatorcomprises two electrode portions.
 6. The thin film piezoelectric deviceaccording to claim 1, wherein the piezoelectric laminated structurecomprises a lower electrode constituting the metal electrode, a firstpiezoelectric film, an inner electrode constituting the metal electrode,a second piezoelectric film, and an upper electrode constituting themetal electrode stacked in order from the substrate side in at least onethin film piezoelectric resonator.
 7. The thin film piezoelectric deviceaccording to claim 1, wherein at least one insulating layer of siliconoxide and/or silicon nitride and/or aluminum nitride as a main componentis attached to the diaphragm.
 8. The thin film piezoelectric deviceaccording to claim 1, wherein an insulating layer comprising at leastone layer of silicon oxide and/or silicon nitride and/or aluminumnitride as a main component intervenes only between the support area ofthe piezoelectric laminated structure and the substrate.
 9. The thinfilm piezoelectric device according to claim 1, wherein thepiezoelectric film is an oriented crystal film represented by a generalformula Al.sub.1-xGa.sub.xN (where 0<x<1) and consists of a solidsolution of aluminum nitride and gallium nitride showing a c-axisorientation, and a rocking curve half value width (FWHM) of adiffraction peak of a (0002) surface of the film is 3.0.degree. or lessin at least one thin film piezoelectric resonator.
 10. The thin filmpiezoelectric device according to claim 1, wherein the piezoelectricfilm is a zinc oxide thin film showing a c-axis onentation, and arocking curve half value Width (FWM) of a diffraction peak of a (0002)surface of the film is 3.0.degree. or less in at least one thin filmpiezoelectric resonator.
 11. The thin film piezoelectric deviceaccording to claim 1, wherein the piezoelectric film is a lead titanatethin film or a lead zirconate titanate thin film in at least one thinfilm piezoelectric resonator.
 12. The thin film piezoelectric deviceaccording to claim 1, wherein the planar shape of one of the diaphragmshas two pairs of opposite sides, and at least one pair of opposite sidesis formed to be non-parallel in at least one thin film piezoelectricresonator.
 13. The thin film piezoelectric device according to claim 1,wherein at least a part of the planar shape of one of the diaphragms isformed by a non-square irregular polygonal shape in at least one thinfilm piezoelectric resonator.
 14. The thin film piezoelectric deviceaccording to claim 1, wherein the planar shape of one of the diaphragmsis formed, by a non-square irregular polygonal shape including a curvedportion in at least a part of the shape in at least one thin filmpiezoelectric resonator.
 15. The thin film piezoelectric deviceaccording to claim 1, the thin film piezoelectric device being a thinfilm piezoelectric filter.
 16. The thin film piezoelectric deviceaccording to claim 15, wherein the thin film piezoelectric filtercomprises a ladder type circuit comprising a plurality of thin filmpiezoelectric resonators connected in series and at least one of thethin film piezoelectric resonators branched from/connected to theplurality of resonators connected in series.
 17. The thin filmpiezoelectric device according to claim 1, the thin film piezoelectricdevice being a duplexer comprising a plurality of thin filmpiezoelectric filters.
 18. The thin film piezoelectric device accordingto claim 17, wherein the thin film piezoelectric filter comprises aladder type circuit comprising a plurality of thin film piezoelectricresonators connected in series and at least one of the thin filmpiezoelectric resonators branched from/connected to the plurality ofresonators connected in series.
 19. A method of manufacturing the thinfilm piezoelectric device according to claim 1, comprising the steps of:forming the piezoelectric laminated structure on the substratecomprising a semiconductor or an insulator; and thereafter forming thevibration spaces in the substrate from a side opposite to the side onwhich the piezoelectric laminated structure is fabricated by a deepgraving type reactive ion etching process.
 20. The thin filmpiezoelectric device according to claim 2, wherein the ratio D1/D0 is ina range of 0.18 to 0.3 with respect to all the sets of two electricallyconnected-adjacent thin film piezoelectric resonators.
 21. The thin filmpiezoelectric device according to claim 7, wherein assuming that athickness of the piezoelectric film is t, and a thickness of theinsulating layer is t′, 0.1.ltoreq.t′/t.ltoreq.0.5 is satisfied.
 22. Thethin film piezoelectric device according to claim 1, wherein at leastone of metal electrodes comprises a main electrode layer and an adhesivelayer.
 23. The thin film piezoelectric device according to claim 1,wherein a thickness of the piezoelectric film is in a range of 0.98 to1.57 .mu.m.
 24. The thin film piezoelectric device according to claim 1,wherein the piezoelectric laminated structure comprises a lowerelectrode constituting the metal electrode, the piezoelectric film, andan upper electrode constituting the metal electrode stacked in orderfrom the substrate side, and a total of thicknesses of the lowerelectrode and the upper electrode is in a range of 320 to 485 nm. 25.The thin film piezoelectric device according to claim 24, wherein athickness of the lower electrode is in a range of 170 to 235 nm.
 26. Thethin film piezoelectric device according to claim 24, wherein athickness of the upper electrode is in a range of 150 to 250 nm.
 27. Thethin film piezoelectric device according to claim 1, wherein thepiezoelectric laminated structure comprises a lower electrodeconstituting the metal electrode, the piezoelectric film, and an upperelectrode constituting the metal electrode stacked in order from thesubstrate side, and a ratio of a total of thicknesses of the lowerelectrode and the upper electrode to a thickness of the piezoelectricfilm is in a range of 0.255 to 0.392.
 28. The thin film piezoelectricdevice according to claim 22, wherein the piezoelectric laminatedstructure comprises a lower electrode constituting the metal electrode,the piezoelectric film, and an upper electrode constituting the metalelectrode stacked in order from the substrate side, and a ratio of atotal of thicknesses of the lower electrode and the upper electrode to athickness of the piezoelectric film is in a range of 0.255 to 0.452. 29.A thin film piezoelectric device including a substrate having aplurality of vibration spaces, an insulating layer formed on an uppersurface of the substrate, a piezoelectric laminated structure formed onan upper surface of the insulating layer, diaphragms positioned facingthe vibration spaces, and a support area in which the piezoelectriclaminated structure and the insulating layer are supported by thesubstrate, a plurality of thin film piezoelectric resonators beingformed facing the vibration spaces, wherein the piezoelectric laminatedstructure has at least a piezoelectric film and a metal electrode formedon at least a part of each of the opposite surfaces of the piezoelectricfilm, each diaphragm comprises a portion of the piezoelectric laminatedstructure and a portion of the insulating layer, and a support areacomprises another portion of the piezoelectric laminated structure andat least a portion of the insulating layer, and wherein at least one setof two adjacent thin film piezoelectric resonators are electricallyconnected to each other through the metal electrode, the thin filmpiezoelectric device comprising at least one set of two adjacent thinfilm piezoelectric resonators in which D0 is a distance between thecenters of the diaphragms of the two electrically connected adjacentthin film piezoelectric resonators and D1 is a length of a segment ofthe support area on a straight line passing through centers of thediaphragms of two electrically connected adjacent thin filmpiezoelectric resonators, and a ratio DI/DO is 0.1 to 0.5.
 30. The thinfilm piezoelectric device according to claim 29, wherein the ratio D1/D0is in a range of 0.1 to 0.5 with respect to all the sets of twoelectrically connected adjacent thin film piezoelectric resonators. 31.The thin film piezoelectric device according to claim 29, wherein eachof the vibration spaces is formed by a via hole extending from thesurface of the substrate on which the insulating layer is formed to theopposite surface, and a side wall surface of the via hole forms a slantangle in a range of 80 to 100° with respect to the surface of thesubstrate on which the insulating layer is formed.
 32. The thin filmpiezoelectric device according to claim 29, wherein the piezoelectriclaminated structure comprises a lower electrode constituting the metalelectrode, the piezoelectric film, and an upper electrode constitutingthe metal electrode stacked in order from the insulating layer side inat least one thin film piezoelectric resonator.
 33. The thin filmpiezoelectric device according to claim 32, wherein the upper electrodeof the at least one thin film piezoelectric resonator comprises twoelectrode portions.
 34. The thin film piezoelectric device according toclaim 29, wherein the piezoelectric laminated structure comprises alower electrode constituting the metal electrode, a first piezoelectricfilm, an inner electrode constituting the metal electrode, a secondpiezoelectric film, and an upper electrode constituting the metalelectrode stacked in order from the insulating layer side in at leastone thin film piezoelectric resonator.
 35. The thin film piezoelectricdevice according to claim 29, wherein the insulating layer comprises atleast one layer of silicon oxide and/or silicon nitride and/or aluminumnitride as a main component.
 36. The thin film piezoelectric deviceaccording to claim 29, wherein the piezoelectric film is an orientedcrystal film represented by a general formula Al_(1-x)Ga_(x)N (where0<x<1) and consists of a solid solution of aluminum nitride and galliumnitride showing a c-axis orientation, and a rocking curve half valuewidth (FWHM) of a diffraction peak of a (0002) surface of the film is3.0° or less in at least one thin film piezoelectric resonator.
 37. Thethin film piezoelectric device according to claim 29, wherein thepiezoelectric film is a zinc oxide thin film showing a c-axisorientation, and a rocking curve half value width (FWHM) of adiffraction peak of a (0002) surface of the film is 3.0° or less in atleast one thin film piezoelectric resonator.
 38. The thin filmpiezoelectric device according to claim 29, wherein the piezoelectricfilm is a lead titanate thin film or a lead zirconate titanate thin filmin at least one thin film piezoelectric resonator.
 39. The thin filmpiezoelectric device according to claim 29, wherein the planar shape ofone of the diaphragms has two pairs of opposite sides, and at least onepair of opposite sides is formed to be non-parallel in at least one thinfilm piezoelectric resonator.
 40. The thin film piezoelectric deviceaccording to claim 29, wherein at least a part of the planar shape ofone of the diaphragms is formed by a non-square irregular polygonalshape in at least one thin film piezoelectric resonator.
 41. The thinfilm piezoelectric device according to claim 29, wherein, the planarshape of one of the diaphragms is formed by a non-square irregularpolygonal shape including a curved portion in at least a part of theshape in at least one thin film piezoelectric resonator.
 42. The thinfilm piezoelectric device according to claim 29, the thin filmpiezoelectric device being a thin film piezoelectric filter.
 43. Thethin film piezoelectric device according to claim 42, wherein the thinfilm piezoelectric filter comprises a ladder type circuit comprising aplurality of thin film piezoelectric resonators connected in series andat least one of the thin film piezoelectric resonators branchedfrom/connected to the plurality of resonators connected in series. 44.The thin film piezoelectric device according to claim 29, the thin filmpiezoelectric device being a duplexer comprising a plurality of thinfilm piezoelectric filters.
 45. The thin film piezoelectric deviceaccording to claim 44, wherein the thin film piezoelectric filtercomprises a ladder type circuit comprising a plurality of thin filmpiezoelectric resonators connected in series and at least one of thethin film piezoelectric resonators branched from/connected to theplurality of resonators connected in series.
 46. A method ofmanufacturing the thin film piezoelectric device according to claim 29,comprising the steps of forming the insulating layer on the substratecomprising a semiconductor or an insulator; forming the piezoelectriclaminated structure on the insulating layer; and thereafter forming thevibration spaces in the substrate from a side opposite to the side onwhich the insulating layer is form by a deep graving type reactive ionetching process.
 47. The thin film piezoelectric device according toclaim 30, wherein the ratio D1/D0 is in a range of 0.18 to 0.3 withrespect to all the sets of two electrically connected adjacent thin filmpiezoelectric resonators.
 48. The thin film piezoelectric deviceaccording to claim 29, wherein assuming that a thickness of thepiezoelectric film is t, and a thickness of the insulating layer is t′,0.1≦t′/t≦0.5 is satisfied.
 49. The thin film piezoelectric deviceaccording to claim 29, wherein at least one of metal electrodescomprises a main electrode layer and. an adhesive layer.
 50. The thinfilm piezoelectric device according to claim 29, wherein a thickness ofthe piezoelectric film is in a range of 0.98 to 1.57 μm.
 51. The thinfilm piezoelectric device according to claim 29, wherein thepiezoelectric laminated structure comprises a lower electrodeconstituting the metal electrode, the piezoelectric film, and an upperelectrode constituting the metal electrode stacked in order from theinsulating layer side, and a total of thicknesses of the lower electrodeand the upper electrode is in a range of 320 to 485 nm.
 52. The thinfilm piezoelectric device according to claim 51, wherein a thickness ofthe lower electrode is in a range of 170 to 235 nm.
 53. The thin filmpiezoelectric device according to claim 51, wherein a thickness of theupper electrode is in a range of 150 to 250 nm.
 54. The thin filmpiezoelectric device according to claim 29, wherein the piezoelectriclaminated structure comprises a lower electrode constituting the metalelectrode, the piezoelectric film, and an upper electrode constitutingthe metal electrode stacked in order from the insulating layer side, anda ratio of a total of thicknesses of the lower electrode and the upperelectrode to a thickness of the piezoelectric film is in a range of0.255 to 0.392.
 55. The thin film piezoelectric device according toclaim 49, wherein the piezoelectric laminated structure comprises alower electrode constituting the metal electrode, the piezoelectricfilm, and an upper electrode constituting the metal electrode stacked inorder from the insulating layer side, and a ratio of a total ofthicknesses of the lower electrode and the upper electrode to athickness of the piezoelectric film is in a range of 0.255 to 0.452.